Albert Barnes on Titus 3:9

But avoid foolish questions and genealogies. 1Timm 1:4; 2Ti 2:16, 2Ti 2:23.

And contentions, and strivings about the law. Such as the Jews started about various matters connected with the law--about meats and drinks, etc. 1Timm 1:4. Comp. Acts 18:15.

For they are unprofitable and vain. They disturb and embitter the feelings; they lead to the indulgence of a bad spirit; they are often difficult to be settled, and are of no practical importance if they could be determined. The same thing might be said of multitudes of things about which men dispute so earnestly now.

(c) "avoid foolish" 2Ti 2:23