17 By faith Abraham, when he was tested, offered up Isaac, and he who had received the promises offered up his only begotten son,
Faith functions in a variety of ways. We see this in Hebrews 17-40. Verses 17-22 is one unit. Verses 17-19 presents Abraham’s faith.
17 By faith Abraham,
Abraham was willing to offer his son Isaac sacrificially at God’s request.
when he was tested,
God “tested” Abraham to prove the reality of his faith. The Greek word “tried” indicates that at the very point of testing, Abraham offered Isaac (Ge 22:1-5).
You can see James’ treatment of Abraham here: https://versebyversecommentary.com/james/james-221/
offered up Isaac,
The word “offered” has a sacrificial implication. Genesis 22:16-18 records the event of offering up of Isaac. Note my study of James 2:21-24 on further biblical comment on this event.
and he who had received the promises offered up
Abraham welcomed God’s promise to him and thus freely offered up his son Isaac on an altar. This put a conflict between God’s promise that Isaac would be his heir and the command to put him to death. Abraham could have asked: “If God planned to use Isaac as the means of his posterity, then why should he be killed?”
his only begotten [unique] son,
The Greek term for “begotten” carries the idea of unique or special (Jn 1:18; 3:16). Isaac was one-of-a-kind. He is the one who will continue the line of the Messiah. Abraham was the father of both Isaac and Ishmael, but Isaac was unique because he was the heir of the promise. The linage of the Messiah would come from Abraham through Isaac. This was a test of Abraham’s human love for his son and his belief in God’s promises. Which would prevail?
The Father called the incarnate Christ His “only begotten Son.” Isaac was a type of Christ because he was uniquely born from parents of very old age. He was not the only son of Abraham and Sarah because they had another son by the name of Ishmael. God, however, excluded Ishmael from the Abrahamic Covenant because he was the son of the Egyptian Hagar. Thus, he could not be part of the Jewish line from Abraham.
Faith reconciles the love of God with the providence of God.
Abraham waited 25 years for Isaac to be born around whom God would pass the Abrahamic Covenant. The test of faith of Abraham was not his love for Isaac; the test brought his love for Isaac into conflict with God’s promise. If the Abrahamic Covenant was to be fulfilled through Isaac, why would God ask Abraham to sacrifice him on an altar? Abraham refused to accept the idea that God was inconsistent with His promises. We, as well, must believe that God will be true to His word. “Great is your faithfulness.” It is important to believe in God’s consistency.