Charles H. Spurgeon on Psalms 59:17

Unto thee, O my strength, will I sing. Formerly he had said that the strength of his enemy was with God, and now he asserts the same thing of his own. The expression, however, which admits of two meanings, he elegantly applies to himself in a different sense. God has the strength of the wicked in his hands, to curb and to restrain it, and to show that any power of which they boast is vain and fallacious. His own people, on the other hand, he supports and secures against the possibility of falling, by supplies of strength from himself. John Calvin.