There has been some critical teaching going around of how God promised Abram a son, but he took matters into his own hands and at the wishes of Sarai, went in to Hagar and begat Ishmael. It has been said that Abram did not wait on God’s timing, but how he decided to “help God along” by going in to Hagar.
But today the Lord told me to go back over these chapters and He would clarify all this. In Genesis 18:19, God spoke of His trust in Abraham, saying, “For I know him, that he will command his children and his household after him, and they shall keep the way of the Lord, to do justice and judgment, that the Lord may bring upon Abraham that which He hat spoken of him.” Now, if Abram, and later called Abraham, was not faithful, God would not have said this of him.
For when we look in Genesis 15:3-4, it is written, “And Abram said, Behold, to me thou has given no seed: and, lo, one born in my house is mine heir. And behold, the word of the Lord came unto him, saying, This shall not be thine heir; but he that shall come forth out of thine own bowels shall be thine heir.”

If you notice, all God said to Abram at that time was that he will be the father of a son. God did not at that time say Sarai would be the mother of that child. Some have made the wrong assumption here, and therefore comes the erroneous teaching that Abram “missed it”. In Genesis chapter 16, Sarai told Abram to go into Hagar and take her for wife, and she bore Abram’s firstborn son, Ishmael. Thus, the birth of Ishmael fulfilled the first promise of a son to Abram. And although Ishmael was not the son of covenant that God said he would make with Isaac, he was, nonetheless the fulfillment of that promise, that Abram would be the father of a son.
Later, in Genesis 17, the covenant of circumcision was made between God and Abram, when Abram was 99 and Ishmael was 13 years old. Also, here in chapter 17, God changed Abram’s name, which meant “Exalted Father”, to Abraham, which means “Father of a multitude”. And He changed Sarai’s name to Sarah, which is a royal name given as to a Queen or to a lady of nobility.

It was here, and not before, that God told Abraham that He would give him also a son of her. And of course, that son was Isaac, whose name meant “laughter”, for Sarah laughed when the Angel of the Lord said she would bear a son in her old age. In Genesis 17:21, God said, “But My covenant will I establish with Isaac, which Sarah shall bear unto thee at this set time in the next year.” At that time, Abraham took Ishmael his son, and all the males that were born in his house, or bought with money, and circumcised them all, and he himself was too.
Here’s something else I want to add, in Chapter 17:17, Abraham fell upon his face and laughed and said in his heart, “Shall a child be born unto him that is a hundred years old? and shall Sarah, that is ninety years old, bear? God said Sarah thy wife shall bear thee a son indeed. God imputed no guilt to Abraham at all in this, it was a laugh of faith and joy.
 But in Genesis 18:12-15 it says, “Therefore Sarah laughed within herself, saying, After I am waxed old shall I have pleasure, my lord being old also? And the Lord said unto Abraham, Wherefore did Sarah laugh, saying, Shall I of a surety bear a child, which am old?
Is anything too hard for the Lord? At the time appointed I will return unto thee, according to the time of life, and Sarah shall have a son. Then Sarah denied, saying, I laughed not; for she was afraid. And He said, Nay, but thou didst laugh.” Sarah laughed in disbelief, then lied to God about it. The blood offering of the calf Abraham had prepared covered her sin, in Genesis 18:7, by the way, for Sarah did sin by denying she laughed.
We do find, however, in Genesis 12 and again in Genesis 20, that Abraham seemingly stepped out of faith by having Sarah tell people she was Abraham’s sister, instead of his wife, in order to save his own life, for he perceived men would kill him for his wife’s sake, that they might have her. And this was a half-truth, because Sarah was indeed his half-sister, the daughter of his father, but not the daughter of his mother. And twice it nearly Abraham his wife, had God not stepped in to correct the situation, and saw to it that Sarah was not defiled, for, through them would be born the Son of Covenant, Christ Jesus.
Isn’t it wonderful how God will take situations in which we do err, to turn to our own good, when we love Him and serve Him? God knew Abraham loved Him, and God covered his mistakes to show His great mercy, not only to Abraham, but to us today.
Did Abraham do everything in faith? Well it would seem that in these two instances Abraham got off into the flesh, instead of trusting God to protect his life. But both times, God greatly increased Abraham’s riches, so even in his error, God caused great blessing to come upon him. For God knew Abraham was faithful. And that faithfulness was shown in Genesis 22, where God asked Abraham to sacrifice Isaac, and though it was not what Abraham wanted to do, nonetheless, he withheld not his beloved Isaac from the Lord. At the last second, after Abraham had bound Isaac to the altar, God provided a ram for the sacrifice instead. By this, God knew that Abraham feared Him, seeing he had not withheld his son, his only son, from Him. God used that pattern later to sacrifice His only begotten Son for us that we might be made the righteousness of God through Christ Jesus.
So the question is not, have you made mistakes, but rather, are you faithful? Can God look at you and say He finds you faithful and He knows you will teach all your household the way of the Lord, to do justice and judgment? Because, you see, if you are faithful, God will see to it that even your mistakes turn out right!