John Calvin Commentary Romans 12:11

"in diligence not slothful; fervent in spirit; serving the Lord;" — Romans 12:11 (ASV)

Not slothful in business, etc. This precept is given to us, not only because a Christian life ought to be an active life, but because it often requires us to overlook our own benefit and to spend our labors for our brothers and sisters. In a word, we ought in many things to forget ourselves; for unless we are in earnest and diligently strive to shake off all sloth, we will never be rightly prepared for the service of Christ.

By adding fervent in spirit, he shows how we are to attain the former; for our flesh, like the donkey, is always sluggish and therefore needs goads; and it is only the fervor of the Spirit that can correct our slothfulness. Hence, diligence in doing good requires that zeal which the Spirit of God kindles in our hearts. Why then, someone may say, does Paul exhort us to cultivate this fervor? To this I answer—that though it is the gift of God, it is yet a duty enjoined upon the faithful to shake off sloth and to cherish the flame kindled by heaven, as it usually happens that the Spirit is suppressed and extinguished through our own fault.

The third point, serving the time, is to the same effect: for as the course of our life is short, the opportunity for doing good soon passes away, and therefore we should show more eagerness in performing our duty. So Paul instructs us in another place to redeem the time, because the days are evil. The meaning may also be that we ought to know how to adapt ourselves to the time, which is a matter of great importance. But Paul seems to me to contrast what he commands about serving the time with idleness.

However, since κυρίῳ, the Lord, is read in many old copies, though it may seem at first sight unrelated to this passage, I still dare not wholly reject this reading. And if this reading is accepted, Paul, I have no doubt, meant to refer the duties to be performed towards brothers and sisters, and whatever served to cherish love, to a service done to God, so that he might add greater encouragement to the faithful.