“Isaiah, you mark my words. Before that baby is able to say ‘momma’ or ‘daddy’ Samaria and Damascus will be poor.”
So Isaiah recorded the prophecy, just as God had told him to do.
What was the purpose of that? Was it so that God would have something to jog His memory?
Of course not.
It was for the benefit of Isaiah, the Israelite people and anyone else that wanted to know.
The record was concrete evidence for them to look back on and learn that God always makes good on His promises.
It was recorded so it could be an aid to their faith.
Promises of God fill the Word. Search them out. Know they are true. Record what the Lord has promised you and then note when it comes to pass. Look back to it when you’re in need of encouragement.
Because God is always faithful.