Charles H. Spurgeon on Psalms 108:10

The strong city built on the rock, even man's hardened heart, stronger and more stony than the tomb, he had conquered and overcome; and in him and his might are his people to carry on his warfare, and to cast down all the strongholds of human pride, and human stubbornness, and human unrepentance. —Plain Commentary.

Verses 10-11. It is not conclusive evidence that we are not called to undertake a given work or perform a certain duty, because it is very difficult, or even impossible for us to succeed without special help from God. If God calls David to take Petra, he shall take Petra. —William S. Plumer.