Would you know? asks William Law, in his beautiful chapter on singing psalms — would you know who is the greatest saint in the world? Well, it is not he who prays most or fasts most; it is not he who gives most alms, or is most eminent for temperance, chastity, or justice; but it is he who is always thankful to God, who wills everything that God wills, and who receives everything as an instance of God's goodness, and has a heart always ready to praise God for His goodness. 

And then Law winds up with this, and I wish it would send you all to the golden works of that grace-laden writer: 

Sometimes, he adds, imagine to yourselves that you saw holy David with his hands upon his harp, and his eyes fixed" upon heaven, calling in transport upon all creation, sun and moon, light and darkness, day and night, men and angels, to join with his rapturous soul in praising the Lord of heaven. 

Dwell upon this imagination till you think you are singing with this Divine musician; and let such a companion teach you to exalt your heart unto God every new morning in his thanksgiving psalms. 

Or make a morning psalm suitable to your own circumstance out of David's great thanksgiving psalms. You should take the finest and the selectest parts of David's finest and selectest psalms, and adding them together make them every morning more and more fit to express your own thankful hearts.