John Calvin Commentary Psalms 31:3

"For thou art my rock and my fortress; Therefore for thy name`s sake lead me and guide me." — Psalms 31:3 (ASV)

For you are my rock. This verse may be read as one sentence, as follows: Since you are like a tower for my defense, for your name’s sake direct and guide me throughout my whole life. And so the conjunction, as in many similar cases, would be superfluous. But I prefer a different interpretation: namely, that David, by interjecting this reflection, encourages himself not only to be earnest in prayer but also to have a confident hope of obtaining his requests.

We know, in any case, that it is usual for him to include such things in his prayers as may serve to remove his doubts and to confirm his assurance. Therefore, having expressed his need, he assures himself—to encourage and uplift himself—that his prayer will certainly receive a favorable answer.

He had formerly said, Be my strong rock and fortress; and now he adds, Assuredly you are my rock and my fortress, implying that he did not speak these words rashly, like unbelievers, who, although they are accustomed to ask much from God, are kept in suspense by the dread of uncertain events.

From this he also draws another encouragement: that he will have God as his guide and governor throughout the whole course of his life. He uses two words, lead and guide, to express the same thing, and he does this (at least, this is how I explain it) because of the various misfortunes and unpredictable changes by which people's lives are tested. It is as if he had said, "Whether I must climb the steep mountain, or struggle through rough places, or walk among thorns, I trust that you will be my continual guide."

Moreover, since people will always find reasons for doubt within themselves if they look to their own merits, David expressly asks that God would be moved to help him for His own name’s sake, or out of regard for His own glory. For, properly speaking, there is nothing else that can move Him to help us. Therefore, it must be remembered that God’s name, as opposed to any merit whatsoever, is the only source of our salvation.

In the next verse, under the metaphor of a net, he appears to refer to the snares and cunning schemes with which his enemies surrounded him.

We know that conspiracies were frequently formed against his life, which would have left him no room for escape. Since his enemies were deeply skilled in strategy and, hating him with an inconceivable hatred, were eagerly bent on his destruction, it was impossible for him to be saved from them by any human power.

On this account, he calls God his strength, as if he had said, "He alone is sufficient to tear apart all the snares in which He sees His afflicted people entangled."