Proverbs 15:26

The former part of this verse speaks of thoughts, the latter of words, but they come all to one; for thoughts are words to God, and words are judged of by the thoughts from which they proceed, so that, 1. The thoughts and words of the wicked, which are, like themselves, wicked, which aim at mischief, and have some ill tendency or other, are an abomination to the Lord; he is displeased at them and will reckon for them. The thoughts of wicked men, for the most part, are such as God hates, and are an offence to him, who not only knows the heart and all that passes and repasses there, but requires the innermost and uppermost place in it. 2. The thoughts and words of the pure, being pure like themselves, clean, honest, and sincere, are pleasant words and pleasant thoughts, well-pleasing to the holy God, who delights in purity. It may be understood both of their devotions to God (the words of their mouth and the meditations of their heart, in prayer and praise, are acceptable to God, Psa 19:14; Psa 69:13) and of their discourses with men, tending to edification. Both are pleasant when they come from a pure, a purified, heart.

— Matthew Henry's Concise Commentary (public domain)

are pleasant words--that is, pleasing to God (Pro 8:8-9).

— Jamieson-Fausset-Brown Commentary (public domain)