Paul wanted his audience to be as diligent in their walk in his absence as much as in his presence (v. 12) – the same obviously holds true as regards the Lord, for he is ever present. Biblical salvation only begins with regeneration, we must carry through to attain that definitive sanctification we have in Christ, through the progressive influence of the word and the Spirit. It is God who is at work in us, so that we can work on ourselves (v. 13). No one can do this on their own. The motivation for God is his own good pleasure, and so it should also be ours.