“Wherewithal [how] shall a young man cleanse his way? by taking heed thereto according to thy word.” — Psalm 119.9
1. A weighty question asked. By what means may the next generation be made better than this? Wherewithal [how] shall a young man cleanse his way? Cleansing implies that it is polluted. Besides the original corruption we all brought into the world with us (from which we are not cleansed unto this day), there are many particular sins which young people are subject to, by which they defile their way, youthful lusts (2 Tim. ii. 22); these render their way offensive to God and disgraceful to themselves. Young men are concerned to cleanse their way—to get their hearts renewed and their lives reformed, to make clean, and keep clean, from the corruption that is in the world through lust, that they may have both a good conscience and a good name. Few young people do themselves enquire by what means they may recover and preserve their purity; and therefore David asks the question for them.
2. A satisfactory answer given to this question. Young men may effectually cleanse their way by taking heed thereto according to the word of God; and it is the honour of the word of God that it has such power and is of such use both to particular persons and to communities, whose happiness lies much in the virtue of their youth. (1.) Young men must make the word of God their rule, must acquaint themselves with it and resolve to conform themselves to it; that will do more towards the cleansing of young men that the laws of princes or the morals of philosophers. (2.) They must carefully apply that rule and make use of it; they must take heed to their way, must examine it by the word of God, as a touchstone and standard, must rectify what is amiss in it by that regulator and steer by that chart and compass. God’s word will not do without our watchfulness, and a constant regard both to it and to our way, that we may compare them together. The ruin of young men is either living at large (or by no rule at all) or choosing to themselves false rules: let them ponder the path of their feet, and walk by scripture-rules; so their way shall be clean, and they shall have the comfort and credit of it here and for ever.
—Matthew Henry on Psalm 119