"When, therefore, God marks out our life, he does not look to what we can do, but requires from us what is above our strength, that we may learn to ask from him power to accomplish it."

     John Calvin, Commentary on the First Epistle to the Thessalonians (1551) at 3:12, trans. Pringle.  =CO 52, col. 159 (cols. 133-180):

Ergo Deus quum vitam nostram format, non respicit quid possimus, sed quod supra vires nostras est, a nobis exigit:  ut a se petere discamus praestandi facultatem.