The problem is that Jesus has gone from us. We can no longer encounter him in the way his contemporaries did. But we are not left with a mere "spiritual" communion:
Because God loves man and has a sovereign respect for our earthbound humanity - for our reality as persons who in their own bodiliness live in a world of people and of things, and thereby grow to spiritual maturity - God always offers us the kingdom of heaven in an earthly guise.How are we to encounter Christ, then, since he has gone from us? Through the "separated sacraments".
If Christ does not show himself to us in his own flesh, then he can make himself visibly present to and for us earthbound men only by taking up earthly non-glorified realities into his glorified saving activity. This earthly element replaces for us the invisibility of his bodily life in heaven. This is precisely what the sacraments are: the face of redemption turned visibly towards us, so that in them we are truly able to encounter the living Christ. The heavenly saving activity, invisible to us, becomes visible in the sacraments.Schillebeeckx illustrates this by saying that Jesus' twelve disciples were never baptized because they had personally encountered Christ the primordial sacrament. Yet St. Paul, the thirteenth apostle, was baptized, never having encountered Jesus in the flesh. "Sacramentality thus bridges the gap and solves the disproportion between the Christ of heaven and unglorified humanity."
From this account of the sacraments as the earthly prolongation of Christ's glorified bodiliness, it follows immediately that the Church's sacraments are not things but encounters of men on earth with the glorified man Jesus by way of a visible form. On the plane of history they are the visible and tangible embodiment of the heavenly saving action of Christ. They are this saving action itself in its availability to us; a personal act of the Lord in earthly visibility and open availability.