ASV notes on Genesis 17:23

YAHAWAH treated Abraham with respect, He was God and a Spirit but because Abraham had a profound faith in God, God as Spirit could be a personal friend with Abraham, they could walk together as friends. God was Spirit and Abraham flesh, but by faith, Jesus was there, together they could overcome all obstacles that were to come.

The very same day God told Abraham about the circumcision, he acted and did it; all the people in his camp from 8 days and up were circumcised. If God tells you to do something by talking to you, or if He talks to you through His Word, just do it, when? When you hear it or read it. God talks to you by The Holy Spirit, or through the Word. The Word is Jesus talking to you. When God touches you through His Word all three are active in your life, the Father, the Son and The Holy Spirit.