Satan will always try your faith, for lack of a better way of describing it.  There’s a passage in Luke that says it better, Jesus told Peter that Satan desires to SIFT him.  In other words, sifting is pushing something larger through a very small passage, crunching it down forcibly, removing, destroying, reshaping everything upon it until it is small enough to fit through the prescribed opening. That’s what the devil is trying to do to you, to sift you as wheat.  And you’re not the only one he’s doing it to.  Let’s read about it:
Luk 22:31  And the Lord said, Simon, Simon, behold, Satan hath desired to have you, that he may sift you as wheat:
Luk 22:32  But I have prayed for thee, that thy faith fail not: and when thou art converted, strengthen thy brethren.
Luk 22:33  And he said unto him, Lord, I am ready to go with thee, both into prison, and to death.
Luk 22:34  And he said, I tell thee, Peter, the cock shall not crow this day, before that thou shalt thrice deny that thou knowest me.
Luk 22:35  And he said unto them, When I sent you without purse, and scrip, and shoes, lacked ye any thing? And they said, Nothing.
Luk 22:36  Then said he unto them, But now, he that hath a purse, let him take it, and likewise his scrip: and he that hath no sword, let him sell his garment, and buy one.
Luk 22:37  For I say unto you, that this that is written must yet be accomplished in me, And he was reckoned among the transgressors: for the things concerning me have an end.
Luk 22:38  And they said, Lord, behold, here are two swords. And he said unto them, It is enough.
Luk 22:39  And he came out, and went, as he was wont, to the mount of Olives; and his disciples also followed him.
Luk 22:40  And when he was at the place, he said unto them, Pray that ye enter not into temptation.
Luk 22:41  And he was withdrawn from them about a stone’s cast, and kneeled down, and prayed,
Luk 22:42  Saying, Father, if thou be willing, remove this cup from me: nevertheless not my will, but thine, be done.
Luk 22:43  And there appeared an angel unto him from heaven, strengthening him.
Luk 22:44  And being in an agony he prayed more earnestly: and his sweat was as it were great drops of blood falling down to the ground.
Luk 22:45  And when he rose up from prayer, and was come to his disciples, he found them sleeping for sorrow,
Luk 22:46  And said unto them, Why sleep ye? rise and pray, lest ye enter into temptation.

   It was Satan’s intent to put the squeeze on Peter, to force him into a place he didn’t want to be, and because Peter wasn’t as rooted in Christ Jesus as he thought he was, when the pressure was really on, Peter folded like a wet tissue.  As do we when we’re not rooted and settled.  You can’t be unsettled and expect to have settled results.  It was written in James that a person that wavers is unstable in all his ways, and that means unsure, without confidence and direction or purpose, thrown about with every wind of circumstance.  Jesus prayed for Peter that he would become stable and afterward strengthen his brethren.  Thank God, Jesus prays good prayers.  We read in verse 42 that Jesus knew he was about to be crucified, and asked His Father that if He were willing, that cup might pass from Him. 
But nevertheless, Jesus was settled in his purpose of doing His Father’s will, and was willing to go to the cross if that’s what it took.  And that’s exactly what it took.  Now here’s a side note: the devil will try to convice us that being Jesus suffered every sin and every disease, that we have to as well.

   Why sleep ye? rise and pray, lest ye enter into temptation.  Don’t think for a moment that you have “arrived” in your faith.  The devil will keep an eye on you through one of his helpers, and when you let down your guard, he will be there to attack.  Surely you don’t think Satan will attack you where you’re strong.  No, he will look for your weakest area and attack you there.  Maybe it will be sickness, maybe things will start breaking for no apparent reason, costing you money to repair or replace them.  Maybe discouragement or depression will come upon you.  Maybe strife will break out around you.  Whatever weapon he chooses to use against you, it’s because you’re weak in that area.  Now, for example, the devil won’t tempt you to use drugs if you don’t already have a history of that, because it wouldn’t attract you.  If someone had been a thief in the past, the devil will tempt them to steal something at a time when nobody will notice.  He would tempt a person with suicide who has suffered deep depression in the past, as a way out of their suffering.  He would lure someone with pornography, for example, who had sexual perversions in the past.  He wouldn’t tempt a thief with pornography, because that would  not be their weakness, understand?
   When a person is attacked with sickness, it’s because they are not settled in that area of the scripture.  The Bible clearly tells us that Jesus has borne our sicknesses and diseases, that we are healed by His stripes.  If it merely said Jesus had been afflicted with diseases upon the cross, that would not have given us relief from sickness, for it would have meant that He simply shared in our sufferings, being made just as we are, frail and mortal.  But instead it says we are HEALED by His stripes, thereby giving us claim to disease-free life!  But if you aren’t settled in your spirit in that promise, you can’t live in it.  When I say settled, I mean SETTLED!  That means when you say “I’m healed by the stripes of Jesus”, and the devil says, “Think so, huh?  Let me show you a thing or two…”  If you’re settled, you’ll snap right back with, “No devil, I’ll show YOU a thing or two!!”  Just being settles doesn’t mean he won’t test you in that area.  I’m settled in healing, yet I get tested from time to time.  Let me tell you, being settled in healing means your confidence in God’s promise won’t waver when you’re hit with symptoms.  Instead, when the devil comes to try to convince you that somehow God has revoked His promise to you, that you firmly stand your ground, call him a liar, and send him on his way. 
   God assures us victory is ours when we stand firmly on His promises.  Many people think that if they are tried, they have sinned, and God is taking their protection away.  Not so.  You will be tried because you have the promises, and Satan, being a thief, is out to steal them from you and he will keep coming back and coming back from time to time to see if you are tired of defending your territory.  Let me tell you something:  if you snooze, you lose.  That doesn’t mean you can’t sleep at night.  That means when you let down your guard, you will be attacked.  Some attacks are sudden and you don’t have time to prepare for them.  You have to STAY prepared.  Others are more gradual, like seeing your friends or family sick, and gradually, your confidence is shaken in God’s Word, to the point where you almost expect to end up sick like they are. 
    First off, you can’t know what others are believing.  They may tell you they believe, but you aren’t with them in their mind.  People will tell you anything to make you happy, but only they know what’s really in their heart.  I’ve prayed with people for their healing, only to have the Lord tell me later that they just told me they agreed to make me feel good, but they didn’t really believe they were healed.  And they weren’t.  But when you see enough sick people all around you, the devil will work on your mind to try to convince you that you’re next, he’s just been too busy to get to you yet, but you’re number is just about up.  That’s an attack just as much as symptoms are.  The battle is in the mind, it is said, and that is so true. 
The promises are believed or rejected in the mind.  Believe me, the devil will do anything he can to make you doubt God’s promises.  If he can’t make symptoms stick on your body, then he will try to get you doubt your standing with God, so you will doubt your right to the promises.  He’s a sly one, alright. 
Many are sick because they don’t feel worthy of the promises.  Let me tell you something: God didn’t give you the promises because you’re worthy.  HE DID IT BECAUSE IT WAS HIS WILL AND CHOICE TO DO SO!  Don’t think your personal goodness or holiness gets you anywhere with God.  Unless God MAKES you worthy, you don’t have a chance.  Neither do I.  You see, it isn’t what YOU’VE done that gets you healed, it’s what HE has done, by His own free will, I might add.  But the devil will try to work on your “worthiness” to talk you out of the promises, and for the vast majority of people, that works.  He hopes you didn’t see Psalms 103:2:3, “Bless the LORD, O my soul, and forget not all His benefits: who forgiveth all thine iniquities; who healeth all thy diseases.”  You see, God forgave ALL your sins when you asked Him.  All means the total amount of them, past, present, and future.  All.  Even the ones you haven’t committed yet.  Yes, they’re under the blood, they’re forgiven, even though you haven’t even done them yet.  How can that be?  Because God no longer puts sin to your account is the clearest way I know how to express it.  It is written in 1 John 3:2-11,
1Jn 3:2  Beloved, now are we the sons of God, and it doth not yet appear what we shall be: but we know that, when he shall appear, we shall be like him; for we shall see him as he is.
1Jn 3:3  And every man that hath this hope in him purifieth himself, even as he is pure.
1Jn 3:4  Whosoever committeth sin transgresseth also the law: for sin is the transgression of the law.
1Jn 3:5  And ye know that he was manifested to take away our sins; and in him is no sin.
1Jn 3:6  Whosoever abideth in him sinneth not: whosoever sinneth hath not seen him, neither known him.
1Jn 3:7  Little children, let no man deceive you: he that doeth righteousness is righteous, even as he is righteous.
1Jn 3:8  He that committeth sin is of the devil; for the devil sinneth from the beginning. For this purpose the Son of God was manifested, that he might destroy the works of the devil.
1Jn 3:9  Whosoever is born of God doth not commit sin; for his seed remaineth in him: and he cannot sin, because he is born of God.
1Jn 3:10  In this the children of God are manifest, and the children of the devil: whosoever doeth not righteousness is not of God, neither he that loveth not his brother.
1Jn 3:11  For this is the message that ye heard from the beginning, that we should love one another.
   Because God no longer sees you as a sinner, you aren’t a sinner.  It isn’t so much what you do as the decision He made not to see what you do as sin.  What I’m trying to say is what John said: whosoever abides in Him does not sin.  Whosoever sins, does so because they have not seen Him, nor experienced Him.  Because we are no longer sinners, our works change.  Our good works do not bring us the status of “sinlessness”.  We are sinless because God said so, and for no other reason.  But because we are sinless, our works will change.  We will learn to love one another and do good for each other.  But that’s another teaching for another time.  Because of God’s determination to look at the blood of Jesus as the payment for our sins in full, we are effectively removed from the equation, with the exception that we either believe, or we don’t.  If we believe, then we are heir to the promises.  That effectively removes Satan’s ability to convince us we are not worthy of salvation.  God never made “our worthiness” a condition of the promise.  That was the devil’s idea.
   Once we’ve removed “our worthiness” from the conditions of the promises, we can move on to true faith in those promises.  As John said in verse 3, every man that has this hope in himself purifies himself, even as God is pure.  How do you “purify yourself”?  Glad you asked.  First thing, quit calling God a liar.  God is truth, and truth only.  If He said He forgave your sins, then He did.  Stop doubting His Word.  That’s the first step.  Assume your proper place in the body of Christ, one where you are accepted in the beloved, holy, without blame, spot, or wrinkle.  You purify yourself by believing ONLY what God says, and NONE of what the devil says.  In other words, every threat of the devil, every condemnation and feeling of guilt, every doubt of God’s love and provision, automatically go in the trash can.  You don’t dwell on them, ponder them, consider them, nor act on them.  You simply discard them as stinky rubbish.  Gone.  Bye-bye.  Good riddance.
   Now you can move on to “who healeth all thy diseases”.  Once you’ve settled the sinner part, healing is easy.  You might think it’s the other way around, but it isn’t.  Everything in God’s Kingdom has an order to it.  Psalm 103:2-3 is an example of that order.  You progress from “Bless the LORD, O my soul”, thanking Him, praising Him, believing Him, speaking well of Him, to “forget not all His benefits”. What are the benefits? He forgives all our sins, and heals all our diseases. That’s HIS promise, not mine. You can have more than the two listed here.  There are many He would have you enjoy, and these are just the start!  Salvation and healing are a couple big benefits, wouldn’t you say? And life is a whole lot better when you have benefits.