“Let the words of my mouth and the meditation of my heart be acceptable in your sight, O LORD, my rock and my redeemer.” (Psalm 19:14, ESV)
David sings how the skies speak of God, declaring His glory and proclaiming the work of His hands. He sings of the goodness of God’s ordinances, how “the law of the Lord is perfect, reviving the soul.” (Psalm 19:7, NIV) Then he muses, “Who can discern his [own] errors?”; and he prays, “Forgive my hidden faults. Keep your servant from willful sins; may they not rule over me. Then will I be blameless, innocent of great transgression.” (Psalm 19:12-13)
How is this accomplished? Through “the meditation of [the] heart.” Jesus says, “From out of the overflow of the heart the mouth speaks.” (Matthew 12:34)
David recognizes he has hidden faults. His prayer is that the Lord Himself would work to keep David “from willful sins” that these would not “rule over [him].” His hope is to remain relatively free of “great transgression” so that from the overflow of his heart, his mouth will speak what is “acceptable” to God.
Jesus speaks against keeping our outsides clean while allowing what’s inside us to defile our speech and actions. Jesus calls us to make His kingdom our treasure, so that what emerges from us naturally reflects what is in our hearts. Like David, let us rely on God the Holy Spirit to change us from the inside out, not from the outside in.