Charles H. Spurgeon on Psalms 40:7

Lo, I come. Christ's coming in the spirit is a joyful coming. I think this, Lo, I come, expresses 1. Present joy. 2. It expresses certain joy: the Lo, is a note of certainty; the thing is certain and true; and his joy is certain; certain, true, solid joy. 3. It expresses communicative joy; designing his people shall share of his joy, Lo, I come! The joy that Christ has as Mediator is a fulness of joy, designed for his people's use, that out of his fulness we may receive, and grace for grace, and joy for joy; grace answering grace in Jesus, and joy answering joy in him. 4. It expresses solemn joy. He comes with a solemnity; Lo, I come! according to the council of a glorious Trinity. Now, when the purpose of heaven is come to the birth, and the decree breaks forth, and the fulness of time is come, he makes heaven and earth witness, as it were, to his solemn march on the errand: he says it with a loud, Lo! that all the world of men and angels may notice, Lo, I come! And, indeed, all the elect angels brake forth into joyful songs of praise at this solemnity; when he came in the flesh, they sang, "Glory to God in the highest, peace on earth, and good will towards man." Ralph Erskine, 1685-1752.