The Responsorial Psalm for today points to our fulfillment: "Blessed is he who comes in the name of the Lord!" (Psalm 118). He who comes in the name of the Lord is Jesus.
Isaiah 26: 1-6 tells us that if the Lord is in our midst we have "a strong city." We can "trust in the Lord for- ever, for in the Lord God we have an everlasting rock." But we have to open our hearts to him. If we do, then the gates to peace will be open to us: "Open up the gates to let in a nation that is just, one that keeps faith. A nation of firm purpose you keep in peace; in peace for its trust is in you."
Jesus came as the promised "Son of David" to fulfill all of God's promises (see 2 Samuel 7: 11-17). But he does not do this unilaterally, by a divine act of magic. God chooses to make the work of salvation depend on human response, human cooperation (see the invitation to Mary, Luke 1:26-38). The grace to cooperate is given to us, but we must use it.
Matthew 7: 21-27 tells us it is not those who just cry out, "Lord, Lord!" who will enter the kingdom of God, but only those who do the will of the Father. It is true that "in the Lord God we have an everlasting rock," but this does us no good unless we build on it. "Everyone then who hears these words of mine and acts on them will be like a wise man who built his house on rock. The rain fell, the floods came, and the winds blew and beat on that house, but it did not fall, because it had been founded on rock." But those who do not base their lives on Christ's words, those who do not act on them, "will be like a foolish man who built his house on sand."
Jesus came to fulfill all of God's promises to the human race, to offer us total, all-satisfying fulfillment in this life and the next. But to be fulfilled by Jesus we must fill ourselves with his words: read them, reflect on them, accept them as true and build our life on them. We have to let his words be made flesh in us in action.
Jesus said, "I am the Way, the Truth and the Life" (John 14:6). He is the fullness of life for us, but only if we fully accept his truth and faithfully try, at least, to follow his way. If we intend to receive him into our daily lives, to make him welcome, to give him an active part in everything we do - in our home and school and social life, our business and politics - then we can say with true joy and celebration: "Blessed is he who comes in the name of the Lord!"
If you seek fulfillment, seek it where it can be found: Respond to Jesus. During Advent, try to make at least one decision a day based explicitly and consciously on God's word.