Adam Clarke on Psalms 19:14

Let the words of my mouth - He has prayed against practical sin, the sins of the body; now, against the sins of the mouth and of the heart. Let my mouth speak nothing but what is true, kind, and profitable; and my heart meditate nothing but what is holy, pure, and chaste.

Acceptable in thy sight - Like a sacrifice without spot or blemish, offered up with a perfect heart to God.

O Lord, my strength - צורי tsuri, "my fountain, my origin."

My redeemer - גאלי goali, my kinsman, he whose right it is to redeem the forfeited inheritance; for so was the word used under the old law. This prayer is properly concluded! he was weak, he felt the need of God's strength. He had sinned and lost all title to the heavenly inheritance, and therefore needed the interference of the Divine kinsman; of Him who, because the children were partakers of flesh and blood, also partook of the same. No prayer can be acceptable before God which is not offered up in his strength; through Him who took our nature upon him, that he might redeem us unto God, and restore the long-lost inheritance. Lord my helpar and my byer. - Old Psalter. He who is my only help, and he that bought me with his blood. This prayer is often, with great propriety, uttered by pious people when they enter a place of worship.