2:19-21 How are we to understand what Paul says here?

V19 teaches that the truth of God's word is a sure foundation regardless of how many in the church have taught error and shipwrecked their faith, as well as cause others to abandon theirs (CP V17-18; 1Ti 1:19-20).

Paul uses the word vessels metaphorically of the visible church in 2Ti 2:20-21. Not all are sincere Christians "... vessels to honour". Many are false Christians "... vessels to dishonour". God knows those who are His.

They turn away from iniquity and false teaching (CP Jn 10:14; 1Cor 8:3 with 1 Ti 6:3-5, 11).