Albert Barnes Commentary Psalms 119:42

"So shall I have an answer for him that reproacheth me; For I trust in thy word." — Psalms 119:42 (ASV)

So I will have wherewith to answer him that reproaches me - I will have something by which I may reply to those who calumniate me. So the Savior replied to the suggestions of the tempter almost wholly by passages of Scripture (Matthew 4:4, 7, 10); and so, in many cases, the best answer that can be given to reproaches on the subject of religion will be found in the very words of Scripture.

A man of little learning, except what he has derived from the Bible, may often thus silence the cavils and reproaches of the learned skeptic; a man of simple-hearted, pure piety, with no weapon but the word of God, may often thus be better armed than if he had all the arguments of the schools at his command. .

For I trust in your word - I believe it; I rely on it; I confide in it, as my only comfort and protection.