Grace is inactive without our will, hence the order as to "work." "Fear and trembling" simply mean the holy reverence which accompanies obedience (see Eph. I 6:5; I Cor. 2:3; II Cor. 7:15); not slavish fear, like the terror of a mind in danger of condemnation, but 1 anxiety to do what the Lord would have us do, and ; the realization that our own merits are insufficient and 1 we must trust him to give strength for our weakness. The last clause of the sentence (verse 14) confirms this interpretation.