1 After these things the word of the LORD came to Abram in a vision: "Fear not, Abram, I am your shield; your reward shall be very great."
2 But Abram said, "O Lord GOD, what will you give me, for I continue childless, and the heir of my house is Eliezer of Damascus?"
3 And Abram said, "Behold, you have given me no offspring, and a member of my household will be my heir."
4 And behold, the word of the LORD came to him: "This man shall not be your heir; your very own son shall be your heir."
5 And he brought him outside and said, "Look toward heaven, and number the stars, if you are able to number them." Then he said to him, "So shall your offspring be."
6 And he believed the LORD, and he counted it to him as righteousness.
There is no better example of “walking by faith” than that of Abraham, Sarah, Hagar and the conception and birth of Ishmael. It is generally assumed that Abraham and Sarah were in the wrong in putting together a plan to fulfill God’s promises regarding a true heir for Abraham. This is simply not so.
Genesis 16 relates the events:
1 Now Sarai, Abram's wife, had borne him no children. She had a female Egyptian servant whose name was Hagar.
2 And Sarai said to Abram, "Behold now, the LORD has prevented me from bearing children. Go in to my servant; it may be that I shall obtain children by her." And Abram listened to the voice of Sarai.
3 So, after Abram had lived ten years in the land of Canaan, Sarai, Abram's wife, took Hagar the Egyptian, her servant, and gave her to Abram her husband as a wife.
Remember that prior to this, the Lord had promised Abraham that his heir would be of his own flesh and blood. The Lord made no mention of Sarah being the mother of Abraham’s child. In fact He does not do so until long after the birth of Ishmael (Genesis 17:15-21; Hebrews 11:11)
So Abraham and Sarah acting in accordance with the traditions of the culture and times conceived a child through Sarah’s Egyptian slave Hagar.
Once again we must remember that thus far the promise was given only in regard to Abraham’s heir. Sarah being the “owner” of the slave woman could lay claim to the child as hers. Of course the results of this produced ill will between Sarah, Hagar and the child and subsequently lead to the Hagar and Ishmael being cast out much to Abraham’s consternation, but all in agreement with God’s purposes and plans. (Genesis 21:11; Galatians 4:21-31)
The heart of the matter is this; whatever is not of faith is sin, conversely whatever is of faith is not sin.
Now we know when Paul made the statement regarding sin being ANYTHING that is not of faith, he was speaking of food and drink and the taboos and customs regarding such things. However the absolute truth he declares stands in every circumstance. All thought and action not proceeding from the faith is sin. (Romans 14:23b)
Abraham believed God and it was accounted to him as righteousness. Abraham believed God!
Abraham and Sarah acted from faith therefore they did not sin. They simply lacked understanding of God’s thoughts and ways i.e. His will and the outworking of that will.
16 For I am not ashamed of the gospel, for it is the power of God for salvation to everyone who believes, to the Jew first and also to the Greek.
17 For in it the righteousness of God is revealed from faith for faith, as it is written, "The righteous shall live by faith."
Eph 2:10 For we are his workmanship, created in Christ Jesus for good works, which God prepared beforehand, that we should walk in them.
The Lord’s ultimate purpose was to reveal the role of both law and grace in His plan, presented by Paul in Galatians 4. Abraham’s and Sarah’s walk of faith, indeed the faith walk of all the saints, begins in the fact that all works of faith originate in the righteousness of God in Christ through the faith given as gift by God, Christ being both substance and object of that faith.
Romans 12:2 Do not be conformed to this world, but be transformed by the renewal of your mind, that by testing you may discern what is the will of God, what is good and acceptable and perfect.
Abraham and Sarah in testing and discerning, were proving the good,acceptable and perfect will of God, and in so doing were transformed. In Romans 12 Paul is actually describing the faith walk of the saints. If our "obedience" is truly carried out in the faith of the righteous, then God's will is revealed in the earth and He is glorified. These are the works prepared beforehand that we, those of renewed mind, i.e. the transformed, should walk in them.