Moreover, it is not said that Satan, or any mortal man, wrestled with Jacob, but God himself: to teach us that our faith is tried by him; and whenever we are tempted, our business is truly with him, not only because we fight under his auspices, but because he, as an antagonist, descends into the arena to try our strength. This, though at first sight it seems absurd, experience and reason teaches us to be true. For as all prosperity flows from his goodness, so adversity is either the rod with which he corrects our sins, or the test of our faith and patience. And since there is no kind of temptation by which God does not try his faithful people, the similitude is very suitable, which represents him as coming, hand to hand, to combat with them. Therefore, what was once exhibited under a visible form to our father Jacob, is daily fulfilled in the individual members of the Church; namely, that, in their temptations, it is necessary for them to wrestle with God. He is said, indeed, to tempt us in a different manner from Satan; but because he alone is the Author of our crosses and afflictions, and he alone creates light and darkness, (as is declared in Isaiah,) he is said to tempt us when he makes a trial of our faith. 

But the question now occurs, Who is able to stand against an Antagonist, at whose breath alone all flesh perishes and vanishes away, at whose look the mountains melt, at whose word or beck the whole world is shaken to pieces, and therefore to attempt the least contest with him would be insane temerity? But it is easy to untie the knot. For we do not fight against him, except by his own power, and with his own weapons; for he, having challenged us to this contest, at the same time furnishes us with means of resistance, so that he both fights against us and for us. In short, such is his apportioning of this conflict, that, while he assails us with one hand, he defends us with the other; yea, inasmuch as he supplies us with more strength to resist than he employs in opposing us, we may truly and properly say, that he fights against us with his left hand, and for us with his right hand. For while he lightly opposes us, he supplies invincible strength whereby we overcome. It is true he remains at perfect unity with himself: but the double method in which he deals with us cannot be otherwise expressed, than that in striking us with a human rod, he does not put forth his full strength in the temptation; but that in granting the victory to our faith, he becomes in us stronger than the power by which he opposes us. And although these forms of expression are harsh, yet their harshness will be easily mitigated in practice. For if temptations are contests, (and we know that they are not accidental, but are divinely appointed for us,) it follows hence, that God acts in the character of an antagonist, and on this the rest depends; namely, that in the temptation itself he appears to be weak against us, that he may conquer in us. Some restrict this to one kind of temptation only, where God openly and avowedly manifests himself as our adversary, as if armed for our destruction. And truly, I confess, that this differs from common conflicts, and requires, beyond all others, a rare, and even heroic strength. Yet I include willingly every kind of conflict in which God exercises the faithful: since in all they have God for an antagonist, although he may not openly proclaim himself hostile unto them.

Calvin, J., & King, J. (2010). Vol. 2: Commentary on the First Book of Moses Called Genesis (196–197). Bellingham, WA: Logos Bible Software.