Calvin's Institutes, III.6.5
No one in this earthly prison of the body has sufficient strength to press on with due eagerness, and weakness so weighs down the greater number that, with wavering and limping and even creeping along the ground, they move at a feeble rate. Let each one of us, then, proceed according to the measure of his puny capacity and set out upon the journey we have begun. No one shall set it out so inauspiciously as not daily to make some headway, though it be slight. Therefore, let us not cease to so act that we may make some unceasing progress in the way of the Lord. And let us not despair at the slightness of our success; for even though attainment may not correspond to desire, when today outstrips yesterday the effort is not lost. Only let us look toward our mark with sincere simplicity and aspire to our goal; not fondly flattering ourselves, nor excusing our own evil deeds, but with continuous effort striving toward this end: that we may surpass ourselves in goodness until we attain to goodness itself. It is this, indeed, which through the whole course of life we seek and follow. But we shall attain it only when we have cast off the weakness of the body, and are received into full fellowship with him.