Jamieson, Fausset and Brown on Romans 12:11

11. not slothful in business--The word rendered "business" means "zeal," "diligence," "purpose"; denoting the energy of action.

serving the Lord--that is, the Lord Jesus (see Ep 6:5-8). Another reading--"serving the time," or "the occasion"--which differs in form but very slightly from the received reading, has been adopted by good critics [Luther, Olshausen, Fritzsche, Meyer]. But as manuscript authority is decidedly against it, so is internal evidence; and comparatively few favor it. Nor is the sense which it yields a very Christian one.