The difference between having faith in Jesus Christ, and having faith alone in Christ, is simple:
Faith in Jesus Christ is to only do good, and not any evil. We believe Jesus saves us from doing any evil, by giving us grace to only please the Father: By that good faith in Christ, we can walk as He walked.
Jhn 8:29
And he that sent me is with me: the Father hath not left me alone; for I do always those things that please him.
Phl 4:13
I can do all things through Christ which strengtheneth me.
Faith alone in Christ,
apart from works, is only faith that
Christ is God. Being apart from our works, by definition it's not the faith in Christ that always does good.
Faith alone in Christ only
agrees that Christ is God, apart from whether our deeds are good or evil. Whether we are pleasing or displeasing the Father in our deeds, we believe Christ is God, and so are saved and justified by our faith alone. We believe we are pleasing the Father by our faith alone, that that Christ is His Son.
Only having faith that Christ is God without doing good, does not please the Father, no more than the devils that also believe:
Jas 2:19
Thou believest that there is one God; thou doest well: the devils also believe, and tremble.
Believing that Christ is God is certainly better than them that do not believe, and them that believe in another god, but having faith alone in Christ being God, does not justify any man or devil.
The only faith in Christ that saves, is the faith toward God that does good, and does no evil:
Psa 106:3
Blessed are they that keep judgment, and he that is doing righteousness at all times.
1 John{2:29}
If ye know that he is righteous, ye know that every one that is doing righteousness is born of him.
3 John{1:11}
Beloved, follow not that which is evil, but that which is good. He that is doing good is of God: but he that is doing evil hath not seen God.
No man doing unrighteousness is justified by their faith alone in Christ, being by definition without doing good.
1Jo 3:18
My little children, let us not love in word, neither in tongue; but in deed and in truth.
Therefore, are we loving and pleasing God by faith in Christ alone? Or, with deeds that love and please God?
Do we believe Jesus Christ is God? Good. Do we believe Christ saves us whether doing good or evil? The devils also believe.
Do we believe Jesus Christ delivers us from all evil, to only do good and please the Father as the Son? We have the faith in Christ that saves the soul from sinning, and justifies the righteous life with God.
Do we believe we can do righteousness at all times in Christ? We have good faith in Christ. Do we believe we cannot always do good, but will sin like all sinners? Out faith in Christ is not good.
If we do not believe in doing righteousness at all times and walk like Jesus walked, our faith alone that Christ is God, is no better than the unbelievers who also do not believe in always doing good and pleasing the Father like Jesus.