The Greek behind this indicates those who practice these...that is, that is their life. A Christian is not going to practice these.
The NASB renders verse 21 as those who practice such things.
The Greek word used is πράσσω conveying the meaning of:properly, the active process in performing (accomplishing) a deed, and implying what is done as a regular practice – i.e. a routine or habit (cf. R. Trench).
It's not a single act but a lifestyle. Knowing the Greek helps clarify this passage.
IF a single act of sin would nullify your salvation then Paul is in trouble as well as he noted he struggled with something.
Of course there are also the many parables of our Lord that warn about the judgment of one's works. And as you said: "The Scriptures don't contradict themselves." Therefore the false idea of "faith alone" is disproven by Scripture.
Yet, Jesus told the people He met to believe in Him.
When Scripture speaks of judging the works of people it is in consideration of rewards in Heaven...not losing or keeping eternal life.
When Jesus met with Nicodemus what did He tell him?
Believe in Me and do x,y and z and you may inherit eternal life?
No.
He said this:
9Nicodemus said to Him, “How can these things be?”
10Jesus answered and said to him, “Are you the teacher of Israel and do not understand these things?
11“Truly, truly, I say to you, we speak of what we know and testify of what we have seen, and you do not accept our testimony.
12“If I told you earthly things and you do not believe, how will you believe if I tell you heavenly things?
13“No one has ascended into heaven, but He who descended from heaven: the Son of Man.
14“As Moses lifted up the serpent in the wilderness, even so must the Son of Man be lifted up;
15so that whoever believes will in Him have eternal life.
16“For God so loved the world, that He gave His only begotten Son, that whoever believes in Him shall not perish, but have eternal life.
17“For God did not send the Son into the world to judge the world, but that the world might be saved through Him.
18“He who believes in Him is not judged; he who does not believe has been judged already, because he has not believed in the name of the only begotten Son of God.
19“This is the judgment, that the Light has come into the world, and men loved the darkness rather than the Light, for their deeds were evil.
20“For everyone who does evil hates the Light, and does not come to the Light for fear that his deeds will be exposed.
21“But he who practices the truth comes to the Light, so that his deeds may be manifested as having been wrought in God.”
John 3:9-21 NASB
I again will ask, IF it is faith + works, how many "good" works do you have to do?
How do you know you've done the right ones?
Yes, and one who refuses to give them up will not be saved despite his faith. Thus says St. Paul.
A Christian is not going to practice these.
If only this were true. There have always been plenty of Christians who remain attached to sin. Paul is addressing his remarks to Christian believers, not to pagans. But if you were to say that such are not true Christians, then you have just admitted that faith alone is not enough: refraining from sin must be added to it.
IF a single act of sin would nullify your salvation then Paul is in trouble as well as he noted he struggled with something.
Not if he repents of it later and seeks forgiveness. But if one were to commit a grievous sin against God and then refuse to repent, then he would loose his salvation by his own choice.
Yet, Jesus told the people He met to believe in Him.
Agreed, but he also told them to keep the Commandments!
I again will ask, IF it is faith + works, how many "good" works do you have to do?
Your question betrays a complete lack of understanding of Catholic teaching. One does not earn salvation by racking up brownie points through good works. Salvation is a complete gratuitous gift of God. The good works required are keeping one self from sin, or do you believe that one can remain in sin and still be saved by faith alone?
A Christian is not going to practice these.
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You’re making a joke, right? Because you can saunter into any honky-tonk in the country and find them packed with people who claim to have been “saved”, and yet these people (they’re referred to in the Scriptures as SINNERS) are practicing every form of sinful behavior you can imagine. I know, I know, they were never saved in the first place! What nonsense!