“O LORD, who shall sojourn in your tent? Who shall dwell on your holy hill? He who walks blamelessly and does what is right and speaks truth in his heart.”
The 15th psalm is a psalm of instruction that teaches the true understanding of the Law, the truly good life, and true good works. These are all fruits of the Spirit and of faith: to live blameless before God through true faith, to do right to the neighbor, and to turn away from the evil ways and from the hypocrisy of the ungodly, by which they serve God with fraudulent works and omit the true works. This psalm belongs to the Third Commandment, concerning the Sabbath, in which we are to hear and learn God’s Word, and it is in the Third Petition (of the Lord’s Prayer).
O Lord, our gracious and merciful Father, grant us steadfastly to believe in Your Son, Jesus Christ, our Savior; to fearlessly confess Him before men to the reproving of the unbelieving and the wicked. Strengthen us by Your Spirit to walk honestly as in the light of day, both privately and in public. Amen.
(from Reading the Psalms with Luther, pgs. 40-41)