From Paul, a New Testament preacher of Grace, to Timothy:
2 Timothy 3:2-4
For men will be lovers of themselves, lovers of money, boastful, arrogant, abusive, disobedient to their parents, ungrateful, unholy, unloving, unforgiving, slanderous, without self-control, brutal, without love of good, traitorous, reckless, conceited, lovers of pleasure rather than lovers of God, having a form of godliness but denying its power.
2 Timothy 3:14-17
14 But as for you, continue in the things you have learned and firmly believed...
15 From infancy you have known the Holy Scriptures, which are able to make you wise for salvation through faith in Christ Jesus.
16 All Scripture is God-breathed and is useful for instruction, for conviction, for correction, and for training in righteousness, so that the man of God may be complete, fully equipped for every good work.
...again, this is Paul saying this about the only holy scriptures they had at the time: the so called "Law/Torah/OT".
He starts the chapter speaking about those who appear godly, but who deny the power by living ungodly. So Paul concludes the chapter by saying that all of the Torah/OT/Law is to be used by the believer for teaching godliness.
Again, this was instructed by the preacher of Grace, Paul - who was filled with the Holy Spirit, after Pentecost - to Timothy, to preach where he was.
Spirit-filled Paul says the Law/Torah/OT is full-of-use for:
1. Instruction - "This is the proper order of things; i.e. what you're supposed to do vs. not."
2. Conviction - "What you're doing right now is considered sin in Yah's eyes."
3. Correction - "You're in error or inaccurate; here's the proper understanding."
4. Training in Righteousness - "These are the actions you're to repeat as a righteous person."
To "deny the power" means these people have access to the Divine Power but didn't implement it.
So when a believer in Christ uses the Law/Torah/OT to instruct, convict, correct, or train another believer in Christ in what they are to do after salvation it isn't an act of pride, carnality, rejecting Christ, returning to bondage, twisting or deception, implication of a lack of salvation, or an act of offense against the believer in Christ...but an act of obedience to Paul, preacher of Grace...and consequently an act of obedience to the Holy Spirit who was inspiring Paul...and by effect an act of love from the Holy Spirit who purposed the instruction, conviction, correction and training through that messenger.
Yah corrects those He loves (Proverbs 3:12; Hebrews 12:6; Revelation 3:19).
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...It's what a believer in Christ is supposed to do for another believer in Christ, AS LONG AS they're not teaching the believer to perform sacrifices and other levitical blood works/deeds of the Law/Torah/OT, because that's what Christ is doing in heaven with his blood right now...which we can't see...which is why we must have faith in Him for our salvation.
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The Holy Spirit inspired Paul to tell Timothy that without the Law/Torah/OT, a believer in Christ is not complete or fully equipped for every good work that Yah has ordained for them to do.