Charles H. Spurgeon on Psalms 57:1

Be merciful unto me. According to the weight of the burden that grieveth us, is the cry that comes from us. How do poor condemned prisoners cry to their judges, "Have pity upon us, have pity upon us!" David, in the day of his calamities doubles his prayer for mercy: Be merciful unto me, O God, be merciful unto me: for my soul trusteth in thee, etc., Until these calamities be overpast. It was not a single calamity, but a multitude of calamities which compassed David, and therefore he compasseth the Lord about with petitions. His spirit being up in prayer, like a bell that rings out, he strikes on both sides, Be merciful unto me, O God, be merciful unto me. Joseph Caryl.