The middle of this passage is a call to holiness. But how can I be holy? I'm quite aware of my besetting sins: I am less aware of those hidden frailties which drive such. What I do know is that no man fully understands himself. Here Calvin has a trenchant comment.
Beyond all controversy, we are called to holiness. But the question about the calling and duty of Christians is totally different from the question about their power or ability. We do not deny that it is demanded from believers that they purify themselves; but elsewhere the Lord declares that this is their duty, while he promises by Ezekiel that he will send "clean waters, that we may be cleansed." (Ezekiel 36:25.)
Wherefore we ought to supplicate the Lord to cleanse us, instead of vainly trying our strength in this matter without his assistance.
We are called to not be as this world is: the irony, is as the cycle we are in degenerates into irrationality, being not of this world is becoming easier. Any truth is now hated. For God is truth.
14 Remind them of these things, and charge them before God not to quarrel about words, which does no good, but only ruins the hearers. 15 Do your best to present yourself to God as one approved, a worker who has no need to be ashamed, rightly handling the word of truth. 16 But avoid irreverent babble, for it will lead people into more and more ungodliness, 17 and their talk will spread like gangrene. Among them are Hymenaeus and Philetus, 18 who have swerved from the truth, saying that the resurrection has already happened. They are upsetting the faith of some. 19 But God's firm foundation stands, bearing this seal: “The Lord knows those who are his”, and, “Let everyone who names the name of the Lord depart from iniquity.”
20 Now in a great house there are not only vessels of gold and silver but also of wood and clay, some for honourable use, some for dishonourable. 21 Therefore, if anyone cleanses himself from what is dishonourable, he will be a vessel for honourable use, set apart as holy, useful to the master of the house, ready for every good work.
22 So flee youthful passions and pursue righteousness, faith, love, and peace, along with those who call on the Lord from a pure heart. 23 Have nothing to do with foolish, ignorant controversies; you know that they breed quarrels. 24 And the Lord's servant must not be quarrelsome but kind to everyone, able to teach, patiently enduring evil, 25 correcting his opponents with gentleness. God may perhaps grant them repentance leading to a knowledge of the truth, 26 and they may come to their senses and escape from the snare of the devil, after being captured by him to do his will.