For whatever it's worth, I agree with everything in your post except (if I understood you correctly) for the faith part - that instead of it originating from/by a sinner, it is Christ's faith in view, which faith, is imputed to the sinner as a gift, otherwise, salvation couldn't be by grace, and therefore, not a gift as Eph 2:8 tells us it is. Grace, by definition, must be all encompassing, with nothing outside of it nor anything other than it needed for salvation, or it simply isn't by grace.
[Eph 2:8 KJV] 8 For by grace are ye saved through faith; and that not of yourselves: [it is] the gift of God:
[Rom 1:17 KJV] 17 For therein is the righteousness of God revealed from faith to faith: as it is written, The just shall live by faith.
[Phl 3:9 KJV] 9 And be found in him, not having mine own righteousness, which is of the law, but that which is through the faith of Christ, the righteousness which is of God by faith:
[Gal 2:16 KJV] 16 Knowing that a man is not justified by the works of the law, but by the faith of Jesus Christ, even we have believed in Jesus Christ, that we might be justified by the faith of Christ, and not by the works of the law: for by the works of the law shall no flesh be justified.
[Eph 2:8 KJV] 8 For by grace are ye saved through faith; and that not of yourselves: [it is] the gift of God:
[Rom 1:17 KJV] 17 For therein is the righteousness of God revealed from faith to faith: as it is written, The just shall live by faith.
[Phl 3:9 KJV] 9 And be found in him, not having mine own righteousness, which is of the law, but that which is through the faith of Christ, the righteousness which is of God by faith:
[Gal 2:16 KJV] 16 Knowing that a man is not justified by the works of the law, but by the faith of Jesus Christ, even we have believed in Jesus Christ, that we might be justified by the faith of Christ, and not by the works of the law: for by the works of the law shall no flesh be justified.
1Ti 4:2 Speaking lies in hypocrisy; having their conscience seared with a hot iron;
1Ti 4:3 Forbidding to marry, and commanding to abstain from meats, which God hath created to be received with thanksgiving of them which believe and know the truth.
1Ti 4:4 For every creature of God is good, and nothing to be refused, if it be received with thanksgiving:
1Ti 4:5 For it is sanctified by the word of God and prayer.
Jesus said He gives us joy that no man can take away because it is not controlled by us but by Him.
If we encounter a situation we do not like we can lose happiness for a time because it is controlled by us but we cannot lose joy for it is controlled by Jesus.
Which the joy of the LORD is our strength for it helps us to keep loving people, and live for God without being discouraged for we will be persecuted, and face trials.
If it is Christ's faith and not our faith then we cannot depart from that faith for it is controlled by Him.
How did these people depart from the faith if we cannot lose that faith.
Which this is speaking of people leaving the truth of the Bible, and embracing something different which this is speaking of the new age movement that interprets the Bible according to the occult and evolution, and Jesus is not Lord and Savior, but evolved to be an ascended master.
Which their beliefs are of seducing spirits and doctrines of devils for they follow Lucifer which they believe he is a god, and an alien, who gave people intelligence, and will help mankind to have peace, and advance, and evolve to be spiritual, which they talk of the return of the gods.
They do not believe Lucifer is a fallen angel because they do not believe in a God, and when the Bible says he fell they say he descended from Venus to Earth to bring the principle of mind to then then animal-man.
How did they depart from the faith and embrace a different interpretation of the Bible.
Heb 11:1 Now faith is the substance of things hoped for, the evidence of things not seen.
The truth is we have to have faith and believe which Jesus when He was talking to Thomas said blessed is he that has not seen but still believes.