Abraham is one of the three outstanding characters in the Old Testament (the other two are Moses and David).  Genesis 17 tells us that when Abraham was 99 the LORD appeared and said, “I am God Almighty, walk before me and be blameless” that I may make my covenant between me and you …” [v.1,2]
Abraham’s acts of faith were an essential ingredient in following God’s injunction to “walk before me and be blameless.” We read how God changed his name to Abraham saying, “I have made you the father of a multitude of nations” [v.5].  Notice the present tense!  In God’s eyes there is no time, he sees the future as he sees the present, to him they are all one!
Paul understood this when he wrote of believers possessing the same faith as Abraham in Romans ch. 4.  He “is the father of all who believe … who also walk in the footsteps of the faith of our father Abraham … who is the father of us all, as it is written, I have made you the father of many nations’ – in the presence of the God in whom he believed, who gives life to the dead and calls into existence the things that do not exist.” [v.11,12,16,17] – except in the mind of God.
Paul continues, Abraham “grew strong in his faith … fully convinced that God was able to do what he had promised.  That is why his faith was counted to him as righteousness.  But the words ‘it was counted to him’ were not written for his sake alone, but for ours also … who believe … “ [v.20,23,24]  Abraham’s interaction with God is a powerful lesson to us which is further added to as we read Genesis 18.
There we read of “3 men” who come to Abraham and he immediately senses they are angels, one of whom is “the angel of his presence” [Isa. 63 v.9] bearing the name ‘Yahweh’ who says, “Shall I hide from Abraham what I am about to do, seeing that Abraham shall surely become a great and mighty nation, and all the nations of the earth shall be blessed in him? For I have chosen him that he may command his children and his household after him to keep the way of the LORD by doing righteousness …” [v.17-19]
Part of the blameless walk before God is to share the way of God with our children and with others.  The Heb. word for ‘blameless’ does not mean sinless, only Christ was sinless, but the same Heb word is translated as ‘upright’ and ‘in sincerity’ in some places (eg Joshua 24 v.14; 2 Sam 22 v.24,26) – the A V trans. as ‘perfect’ can give us the wrong impression, so let us all aim to follow faithful Abraham and his blameless walk before our God.