Let no man despise thy youth - Act so as to be respected in spite of thy youth (1Co 16:11; Tit 2:15); compare “youthful” as to Timothy (2Ti 2:22). He was but a mere youth when he joined Paul (Act 16:1-3). Eleven years had elapsed since then to the time subsequent to Paul’s first imprisonment. He was, therefore, still young; especially in comparison with Paul, whose place he was filling; also in relation to elderly presbyters whom he should “entreat as a father” (1Ti 5:1), and generally in respect to his duties in rebuking, exhorting, and ordaining (1Ti 3:1), which ordinarily accord best with an elderly person (1Ti 5:19).
be thou an example - Greek, “become a pattern” (Tit 2:7); the true way of making men not to despise (slight, or disregard) thy youth.
in word - in all that thou sayest in public and private.
conversation - that is, “behavior” the Old English sense of the word.
in charity ... faith - the two cardinal principles of the Christian (Gal 5:6). The oldest manuscripts omit, “in spirit.”
in purity - simplicity of holy motive followed out in consistency of holy action [Alford] (1Ti 5:22; 2Co 6:6; Jam 3:17; Jam 4:8; 1Pe 1:22).