Genesis 17:21-23 meaning

Isaac was the child promised to Abraham and Sarah, through him the Israelite nation would be multiplied, and Jesus would be born through his line of descendants, God's covenant I will establish with Isaac (v 21). The time for Isaac's birth was coming soon. In the next chapter God will tell Abraham "Sarah will bear to you at this season next year" (Genesis 18:10, 14). 

When He finished talking with him, God went up from Abraham (v 22). God disappeared from Abraham's sight. Abraham, Ishmael, and every male connected in any way with his household were all circumcised In the very same day. Abraham immediately complied with God's instructions and circumcised the entire male population of his household. Abraham believed that God would intervene and provide a son through Sarah (Romans 4:17-19; Hebrews 11:11-12).