If therefore there are but few singers of divine songs, it is because there are but few whose hearts are raised to that height of piety, as to feel any motions of joy and delight in the praises of God.

   Imagine to yourself that you had been with Moses when he was led through the Red Sea; that you had seen the waters divide themselves, and stand on an heap on both sides; that you had seen them heap up till you had passed through, then let fall upon your enemies; do you think that you should then have wanted a voice or an ear to have sung with Moses, “The Lord is my strength and my song, and he is become my salvation,” etc.? I know your own heart tells you, that all people must have been singers upon such an occasion. Let this therefore teach you, that it is the heart that tunes a voice to sing the praises of God; and that if you cannot sing the same words now with joy, it is because you are not so affected with the salvation of the world by Jesus Christ, as the Jews were, or you yourself would have been, with their deliverance at the Red Sea. . . Thus if you can find a man, whose ruling temper is devotion, whose heart is full of God, his voice will rejoice in those songs of praise, which glorify that God, that is the joy of his heart, though he has neither voice nor ear for other music. Would you, therefore, delightfully perform this part of devotion, it is not so necessary to learn a tune, or practice upon notes, as to prepare your heart; for, as our blessed Lord saith, “Out of the heart proceed evil thoughts, murders,” etc., so it is equally true, that out of the heart proceed holy joys, thanksgiving, and praise. If you can once say with David, “My heart is fixed, O God, my heart is fixed”; it will be very easy and natural to add, as he did, “I will sing, and give praise,” etc. 

A Serious Call to a Devout and Holy Life - William Law