When did God first identify himself as the LORD?

In Genesis 15:2, my English translation of Abram's (Abraham's) words indicates that he used the word GOD (in all upper-case letters) in addressing God, which a Hebrew interlinear translation of that verse indicates is the same word as the Tetragrammaton (YHWH), which is usually translated in English as LORD (again, in all upper-case letters).  How could Abram have addressed God in that way, when God Himself said to Moses in Exodus 6:3 that He had not been known to Abraham, Isaac, or Jacob by that name?  Assuming that Moses wrote Genesis, did he make God's revelation of His name to him retroactive?  Or did Abraham, Isaac, and Jacob use the Tetragrammaton as a name for God without knowing the meaning of it, as God revealed it to Moses?      

Exodus 6:2

ESV - ² God spoke to Moses and said to him, "I am the Lord.

Clarify • Share • Report • Asked July 20 2018 • Tim Maas Supporter