Ever wonder what the relationship is between the new man and the old man as they are both felt to be present in the life of a Christian? Luther explains thus:

If here upon earth, the body is unwilling, not capable of grace and Christ’s leading, it must bear the Spirit, upon which Christ rides, who trains it and leads it along by the power of greace, received through Christ. The colt, ridden by Christ, upon which no on ever rode, is the willing spirit, whom no one before could make willing, tame or ready, save Christ by his grace. However the sack-carrier, the burden-bearer, the old Adam, is the flesh, which goes riderless without Christ; it must for this reason bear the cross and remain a beast of burden.