John Gill Commentary Proverbs 5:18

"Let thy fountain be blessed; And rejoice in the wife of thy youth." — Proverbs 5:18 (ASV)

Let your fountain be blessed. Your wife; make her happy by keeping to her and from others; by behaving in a loving, affable, and respectful manner to her; by living comfortably with her, and providing well for her and her children: or "your fountain shall be blessed," as the Targum; that is, with a numerous offspring, which was always reckoned a blessedness, and was generally the happiness of virtuous women, when harlots were barren;

and rejoice with the wife of your youth; taken to be a wife in youth, and lived with ever since; do not despise her, nor divorce her, even in old age, but delight in her company now as ever; carry it not morosely and churlishly to her, but express a joy and pleasure in her; see (Ecclesiastes 9:9) (Malachi 2:14Malachi 2:15) . Jarchi interprets this of the law learned in youth;

but it might be much better interpreted of the pure apostolic church of Christ, "the beulah", to whom her sons are married, (Isaiah 62:4Isaiah 62:5) ; to whom they should cleave with delight and pleasure, and not follow the antichristian harlot.