John Calvin Commentary Acts 20:36

"And when he had thus spoken, he kneeled down and prayed with them all." — Acts 20:36 (ASV)

And kneeling down. The inward affection is indeed the primary thing in prayer; yet external signs, such as kneeling, uncovering the head, and lifting up the hands, have two uses; the first is that we exercise all our members for the glory and worship of God; secondly, that by this exercise our dullness may be awakened, as it were.

There is also a third use in solemn and public prayer, because by this means the children of God profess their godliness, and one of them encourages another to the reverence of God. And as lifting up the hands is a sign of boldness and a fervent desire, so, to testify to our humility, we fall down on our knees.

But he seals and concludes the sermon he previously delivered with prayer, because we can hope for no profit from our doctrine, apart from the blessing of God. Therefore, if we desire to do any good by teaching, admonishing, and exhorting, let us always end in this manner: namely, with prayer.