I don't accept that assertion. There's no indication in the scriptures that God commanded the offerings from Cain and Abel, or that they were acting in obedience to do it.
That’s exactly what “by faith” means.
God speaks to someone to do something.
They now have faith by hearing God’s word.
When they obey what God has said for them to do, then the faith they received by hearing, becomes activated (made alive; made complete) to produce the intended divine result.
IOW, faith without the corresponding action of obedience is dead, dormant, inactive, just as a body without a spirit is dead.
Examples of people operating “by faith”:
#1
By faith Noah, being divinely warned of things not yet seen, moved with godly fear, prepared an ark for the saving of his household, by which he condemned the world and became heir of the righteousness which is according to faith. Hebrews 11:7
God spoke to Noah to build the Ark.
Noah responded in obedience and built the Ark, and was declared righteous; the righteousness according to faith.
#2
By faith Abraham obeyed when he was called to go out to the place which he would receive as an inheritance. And he went out, not knowing where he was going. Hebrews 11:8
This one foreshadows how the Gentiles would be justified by faith by obeying the Gospel.
The Lord called Abraham; to follow Him in the destiny He had for Abraham. Abraham obeyed and justified by faith, foreshadowing salvation by faith.
The only way a person is saved; justified by faith is obedience.
That is why it’s called the “obedience of faith“.
But now is made manifest, and by the scriptures of the prophets, according to the commandment of the everlasting God, made known to all nations for
the obedience of faith: Romans 16:26
Last example; sorry about the long post
Was not Abraham our father
justified by works when he offered Isaac his son on the altar? James 2:21
The works here is not the works of the law, or the work that earns a wage.
The work here that Abraham did, was to obey the Lord and offer his son Isaac on the altar.
This is the obedience of faith. There are many more examples.
Obedience is the principle (law) by which faith operates, and is made complete, to produce the intended divine result.
We receive faith by hearing God speak to us; whether directly or indirectly.
JLB