You teach mans faith is a requirement or condition for ones salvation, thats works/law friend ! Jn 20:31 doesn't say a word about faith being a requirement for salvation.
Matt 23:23
23 Woe unto you, scribes and Pharisees, hypocrites! for ye pay tithe of mint and anise and cummin, and have omitted the weightier matters of the law, judgment, mercy, and faith: these ought ye to have done, and not to leave the other undone.
How do you know you are in Christ ?
You are a new creation in Christ through the new birth when God sealed you with the Holy Spirit after you heard and believed the gospel of your salvation as per Ephesians 1:13. This passage below is evidence/proof that this has taken place in ones life who has been born from above.
2 Corinthians 5:17- Therefore, if anyone is i
n Christ, he is a new creation. The old has passed away; behold, the new has come.
Colossians 3
Since, then, you have been raised with Christ, set your hearts on things above, where Christ is, seated at the right hand of God. 2 Set your minds on things above, not on earthly things. 3 For you died, and your life is now hidden with Christ in God. 4 When Christ, who is your[
a] life, appears,then you also will appear with him in glory.
5 Put to death, therefore, whatever belongs to your earthly nature: sexual immorality, impurity, lust, evil desires and greed, which is idolatry. 6 Because of these, the wrath of God is coming.[
b] 7 You used to walk in these ways, in the life you once lived. 8 But now you must also rid yourselves of all such things as these: anger, rage, malice, slander, and filthy language from your lips. 9 Do not lie to each other, since you have taken off your old self with its practices 10 and have put on
the new self, which is being renewed in knowledge in the image of its Creator. 11 Here there is no Gentile or Jew, circumcised or uncircumcised, barbarian, Scythian, slave or free, but Christ is all, and is in all.
12 Therefore, as God’s chosen people, holy and dearly loved, clothe yourselves with compassion, kindness, humility, gentleness and patience. 13 Bear with each other and forgive one another if any of you has a grievance against someone. Forgive as the Lord forgave you. 14 And over all these virtues put on love, which binds them all together in perfect unity.
15 Let the peace of Christ rule in your hearts, since as members of one body you were called to peace. And be thankful. 16 Let the message of Christ dwell among you richly as you teach and admonish one another with all wisdom through psalms, hymns, and songs from the Spirit, singing to God with gratitude in your hearts. 17 And whatever you do, whether in word or deed, do it all in the name of the Lord Jesus, giving thanks to God the Father through him.
These words may be rendered there is a new creation, i.e. a new creation takes place within him. Whosoever is united to Christ by faith, possesses in himself the gift of a Divine, regenerated, spiritual humanity which Christ gives through his Spirit (cf.
John 5:21;
John 6:33;
John 6:39-40;
John 6:54;
John 6:57;
1 Corinthians 15:45;
1 Peter 1:3;
1 Peter 2:2; and
2 Peter 1:4. Also chap.
2 Corinthians 1:21-22,
2 Corinthians 3:18,
2 Corinthians 4:11,
2 Corinthians 5:5). This life, which he possessed not before, is in fact a new creation of the whole man, “not to be distinguished from regeneration.” Meyer. So also Chrysostom. Cf.
John 1:13;
John 3:3;
John 3:5;
Titus 3:5. The margin of the A. V. renders let him be, which is grammatically admissible, but hardly suits the context.
old things] Literally, the old things. Cf. the ‘old man,’
Romans 6:6;
Ephesians 4:22;
Colossians 3:9; the ‘former conversation’ or manner of living, before the soul was dominated by the Spirit of Christ.
are past away] Literally, passed away, i.e. at the moment of conversion. But as the Dean of Peterborough has shewn in the Expositor, Vol. vii. pp. 261–263, this strict use of the aorist cannot be always pressed in Hebraistic Greek.
behold, all things are become new] Many MSS., versions and recent editors omit ‘all things.’ The passage then stands ‘behold, they are become new.’ If we accept this reading, the passage speaks more clearly of a conversion of the whole man as he is, thoughts, habits, feelings, desires, into the image of Christ. The old is not obliterated, it is renovated. As it stands in the A.V. it relates rather to a substitutionof a new nature for the old.
Isaiah 43:18-19;
Revelation 21:5.Cambridge
Conclusion:
If one is already in Christ prior to hearing and believing the gospel then it's impossible to become a new creation in Christ. See the problem for the calvinist ?
Calvinists have themselves placed in Christ before creation, before they were born, before they heard the gospel, before they believed the gospel and repented of their sins.
hope this helps !!!