The new testament has over 100 "warning" scriptures specifically addressed to Christians. Here are a few examples from Peter.
2 Pet 2:1; But false prophets also arose among the people, just as there will also be false teachers among you, who will secretly introduce destructive heresies, even denying the Master who bought them, bringing swift destruction upon themselves.
2 Pet 2:2; Many will follow their sensuality, and because of them the way of the truth will be maligned;
2 Pet 2:3; and in their greed they will exploit you with false words; their judgment from long ago is not idle, and their destruction is not asleep.
2 Pet 2:4; For if God did not spare angels when they sinned, but cast them into hell and committed them to pits of darkness, reserved for judgment;
2 Pet 2:9; then the Lord knows how to rescue the godly from temptation, and to keep the unrighteous under punishmentfor the day of judgment,
2 Pet 2:10; and especially those who indulge the flesh in its corrupt desires and despise authority. Daring, self-willed, they do not tremble when they revile angelic majesties,
2 Pet 2:12; But these, like unreasoning animals, born as creatures of instinct to be captured and killed, reviling where they have no knowledge, will in the destruction of those creatures also be destroyed,
2 Pet 2:13; suffering wrong as the wages of doing wrong. They count it a pleasure to revel in the daytime. They are stains and blemishes, reveling in their deceptions, as they carouse with you,
2 Pet 2:14; having eyes full of adultery that never cease from sin, enticing unstable souls, having a heart trained in greed, accursed children;
2 Pet 2:15; forsaking the right way, they have gone astray, having followed the way of Balaam, the son of Beor, who loved the wages of unrighteousness;
2 Pet 2:17; These are springs without water and mists driven by a storm, for whom the black darkness has been reserved.
2 Pet 2:18; For speaking out arrogant words of vanitythey entice by fleshly desires, by sensuality, those who barely escape from the ones who live in error,
2 Pet 2:19; promising them freedom while they themselves are slaves of corruption; for by what a man is overcome, by this he is enslaved.
2 Pet 2:20; For if, after they have escaped the defilements of the world by the knowledge of the Lord and Savior Jesus Christ, they are again entangled in them and are overcome, the last state has become worse for them than the first.
2 Pet 2:21; For it would be better for them not to have known the way of righteousness, than having known it, to turn away from the holy commandment handed on to them.
2 Pet 2:22; It has happened to them according to the true proverb, "A DOG RETURNS TO ITS OWN VOMIT," and, "A sow, after washing, returns to wallowing in the mire."
2 Pet 3:10; But the day of the Lord will come like a thief, in which the heavens will pass away with a roar and the elements will be destroyed with intense heat, and the earth and its works will be burned up.
2 Pet 3:11; Since all these things are to be destroyed in this way, what sort of people ought you to be in holy conduct and godliness,
2 Pet 3:14; Therefore, beloved, since you look for these things, be diligent to be found by Him in peace, spotless and blameless,
2 Pet 3:16; as also in all his letters, speaking in them of these things, in which are some things hard to understand, which the untaught and unstable distort, as they do also the rest of the Scriptures, to their own destruction.
2 Pet 3:17; You therefore, beloved, knowing this beforehand, be on your guardso that you are not carried away by the error of unprincipled men and fall from your own steadfastness,
The Schoolmaster is a man's teacher/ruler because of sin; Jesus Christ cannot be according to scripture. Whoever commits sin is under the curse because they've sinned and broke the law (Gal. 3:10).
But that no man is justified by the law in the sight of God, it is evident: for, The just shall live by faith.
And the law is not of faith: but, The man that does them shall live in them.
Only by the law is the knowledge of sin (Rom. 3:20; 7:7).
Anyone that commits sin is "UNDER/JUSTIFIED" by the law.
The "ONLY" way a person can sin is if they are "UNDER" the law.
No man can be "UNDER" the law, and be "UNDER" Jesus Christ.
But if you have respect to persons, you commit sin, and are "convinced of the law" as transgressors. (not of Jesus Christ)
Now we know that what things soever "the law" saith, it saith to them who are "UNDER" the law: that every mouth may be stopped, and all the world may become guilty before God.
1 Corinthians 15:56
The sting of death is sin; and the "strength of sin" is the law.
1 John 3:4
Whosoever commits sin transgresses also the law: for sin is the transgression of the law.
1 John 3:5
And ye know that he was manifested to take away our sins; and in him is no sin.
But before faith came, we were kept under the law, shut up unto the faith which should afterwards be revealed.
Wherefore the law was our schoolmaster to bring us unto Christ, that we might be justified by faith.
But after that faith is come, we are no longer under a schoolmaster.
Once Jesus Christ has come, no believer is under/justified by the law. Because this is true, no man can sin by the law. However, they can commit "unfruitful works" which are understood by faith in Jesus and not by the law.
If a man continues in "unfruitful works" without repentance, they will die and be cast into the furnace of fire of hell.