From Craig Fisher:

Remember, God has already identified himself by connecting himself with the patriarchs Abraham, Isaac and Jacob. When God replies to Moses, “I will be who I will be,” he is referring to that relationship. This is the same usage as Paul’s statement, “I am who I am”, referring to Paul’s history. This statement is a historical identification. It emphasizes that this is a fixed and permanent history, and this emphasis is carried on in the following verses.

God takes on the name, “I AM” to tell the nation of Isreal: ‘I AM has sent me to you.’” (Exodus 3:14) What does this “I AM” mean? God reiterates:

Exo 3:15 Moreover God said to Moses, “Thus you shall say to the children of Israel: ‘The LORD God of your fathers, the God of Abraham, the God of Isaac, and the God of Jacob, has sent me to you. This is My name forever, and this is My memorial to all generations.’

It is clear from the context that “I AM” is the short form for this longer identity. He says “I AM” the God of your fathers. “I AM” is explicitly a historical identity of a personal relationship with his creation.

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