Acts 21:5
And when we had accomplished those days, we departed and went our way; and they all brought us on our way, with wives and children, till we were out of the city: and we kneeled down on the shore, and prayed. And when we had accomplished those days, we departed and went our way; and they all brought us on our way, with wives and children, till we were out of the city: and we kneeled down on the shore, and prayed.
At Tyre, at the close of the seven days, or week, that Paul and his companions spent with the few disciples there on the way to Jerusalem, the farewell described in the verse took place. In that short time Paul had won the deep love of the disciples. At his departure all the brethren, with their wives and children, went with Paul out of the city to the shore and the ship to bring him on his way and conduct him onward.
Before he stepped on board, before parting, they all knelt down together side by side on the shore outside the city and prayed. That kneeling was by disciples before God in worship and petition, by believers kneeling together in prayer. Their prayer was mutual, he praying for them and they praying for him.
Kneeling is the proper and fitting position always when offering prayer to God as the Sovereign of the universe, in both public worship and private worship. The act of bowing down upon the knees shows dependence upon God. Approaching God kneeling shows humility and reverence.