"Christianity is such that its 'theology and ethics' are, by their very nature, inseparable; for it is neither a merely intellectual statement of philosophy nor merely a system of rules for conduct: it is incorporation in Christ, which means faith and practice in one--pattern and power together; mind, will, and emotions working in co-operation" (113).
"Thus, Christian conduct is the result, not simply of the effort to be good, but of incorporation into the Body of Christ" (114).
"St Paul's meaning is evidently something like what Christ dramatically expressed by 'Take up your cross and follow me' (Mark viii. 34, etc.): that is, to follow Jesus means complete devotion, even to the extent of regarding oneself--one's own private desires and ambitions--as 'sentenced to death', or as in fact 'dead'. Yet there is a difference; for whereas Jesus, during his ministry and before his death and resurrection, could only summon disciples ot the effort to 'follow' in obedience, St Paul, called by the risen, heavenly Christ, has found, by incorporation in him, the transforming strength to achieve such devotion. The injunction νεκρώσατε--kill self-centredness--becomes progressively a possibility for those who are united by Baptism with the Body of Christ" (114-115).
Quotations from C.F.D. Moule, The Epistles of Paul the Apostle to the Colossians and to Philemon (Cambridge: 1962) on Colossians 3:5-17.