What the Lord here commands is, that each follower should take up, not his Savior's cross, but his own. The requirement is, that as Christ bore his own cross to his own crucifixion, so his followers should bear each his own cross to his own crucifixion. So the great crucified leader is followed by an endless train of crucified followers. They are crucified symbolically, in all their sufferings of mind or body, in behalf of Christ and of truth. Each follower who hath the spirit of his Master, is crucified in fact or in readiness of spirit. The Spirit of Christ is the spirit of martyrdom.
Commentary on the Gospels, Vol. Matthew-Mark, p. 137 , by D.D. Whedon