The fact of the matter is that the Old Testament text says faith was credited to Abraham as righteousness after Genesis 12.
No it doesn't. Even scholars like Jamieson, Faucett and Brown will disagree with you on this point. You sound like you are making this up as you go along. Hebrews 11 says specifically that he left
his own country. He left it by faith. In order to do so he had to have faith in God, that is he was saved.
In fact, the Old Testament text goes out of its way to demonstrate that Abraham, in fact, had little to no faith in God's promises. We see this in Genesis 12 where God tells Abraham all that He is going to do. Then we see Abraham lying to Pharaoh about Sarah being his wife. Does that demonstrate faith? No, of course not.
1. Abraham had already obeyed God in Gen. 11 and in Gen.12.
2. If the incident in Genesis 12 is an indicator of Abraham's salvation then by the time we get to Genesis 20 Abraham is still not saved for he repeats the very same action with the King of Gerar. Your logic demonstrates you have a belief in sinless perfection. Are you sinless?
How can Abraham believe God--when God tells him that he will become a great nation--and then lie to protect his own life? Really?! How can God's promises be fulfilled if he's dead? He should have known that his life would never be in danger...had he believed God's promises. His lying (and he does this charade twice) demonstrates that he is not, in fact, believing God at that point. Had he believed God, he would not have lied about Sarah being his sister.
Have you not read the Scriptures? You do err not doing so.
But God came to Abimelech in a dream by night, and said to him, Behold, thou art but a dead man, for the woman which thou hast taken; for she is a man's wife. But Abimelech had not come near her: and he said, Lord, wilt thou slay also a righteous nation? Said he not unto me, She is my sister? and she, even she herself said, He is my brother: in the integrity of my heart and innocency of my hands have I done this. (Genesis 20:3-5)
According to you Abraham is still not saved because he is a lying scoundrel. Yet, this is already after the time that he offered Isaac his only son as a sacrifice. You don't make sense.
Your insistence that Abraham had to have faith before leaving Ur is based in your presupposition that God only uses those who first have faith. In fact, almost the entire book of Genesis shows that God chooses faithless people and instills faith into them.
The Archangel
Your presupposition, that God gives faith to unregenerate people comes from Calvin. He learned it from Augustine, not one of the ECF, but rather a Father of the RCC. In the totality of Scripture we see God uses those who put their faith and trust in Him.
For what saith the scripture? Abraham believed God, and it was counted unto him for righteousness. (Romans 4:3)