John Calvin on 1 Corinthians 16:13

13. Watch ye. A short exhortation, but of great weight. He exhorts them to watch, in order that Satan may not oppress them, finding them off their guard. For as the warfare is incessant, the watching requires to be incessant too. Now watchfulness of spirit is this — when, free and disentangled from earthly cares, we meditate on the things of God. For as the body is weighed down by surfeiting and drunkenness, (Luke 21:34,) so as to be fit for nothing, so the cares and lusts of the world, idleness or carelessness, are like a spiritual surfeiting that overpowers the mind. “Sont comme vne yurongnerie spirituelle, qui assopit et estourdit l’entendement;” — “Are like a spiritual drunkenness, which makes the mind drowsy and stupid.”

The second thing is that they persevere in the faith, or that they hold fast the faith, so as to stand firm; because that is the foundation on which we rest. It is certain, however, that he points out the means of perseverance — by resting upon God with a firm faith.

In the third exhortation, which is much of the same nature, he stirs them up to manly fortitude. And, as we are naturally weak, he exhorts them fourthly to strengthen themselves, or gather strength. For where we render it be strong, Paul makes use of only one word, which is equivalent to strengthen yourselves.