Who else is God referring to when he mentions ‘us’? Gen 1:26 ‘ let us make human beings’. Gen 3:22 ‘look humans have become like us’?
There is no doubt in my mind that these are the first references to the fact that our creator God exists in a community called the Trinity. This is a foundational doctrine of the Christian faith, it is not the belief in 3 gods, or the belief that God takes on 3 different shapes or ‘modes’ (a heresy called modalism). Rather, this is the simple yet ineffable idea that God is One AND God is 3, Father, Son, and Holy Spirit. In the Gospel of John Chapter 1, we see that Jesus (described as logos or ‘the Word’) was there at creation:
1In the beginning was the Word, and the Word was with God, and the Word was God. 2He was with God in the beginning. 3Through him all things were made; without him nothing was made that has been made.
Thus, God can have a conversation with himself, because he dwells eternally in the community of Father, Son, and Holy Spirit. In Genesis 1:22 and Genesis 3:22 we get a glimpse of what that conversation looked like.