3, 4. (a) How had Abraham just proved his faith? (b) What was prefigured by this episode?
3 Abraham had just proved that he was willing to sacrifice Isaac, his only son by his first wife, Sarah. (Hebrews 11:17-19; please read Genesis 22:1-18.)
... Some 50 years later, after having seen the tested quality of Abraham’s faith, even in connection with Isaac, Jehovah repeated and enlarged upon this covenant promise, as recorded in Genesis chapter 22.