Here it is, the first of December and the first weekday of Advent, and the liturgy is full of coming and going. Our Advent hymns all seem to be pleas, calling God to "come to us": O Come, O Come, Emmanuel; Come Thou Long Expected Jesus; Savior of the Nations Come... But the readings for today have a totally different angle. The "come" first appears in Isaiah's magnificent prophecy. The "many peoples" of the earth are encouraging one another, "Come, let us climb the Lord's mountain, to the house of the God of Jacob..." It is a proposal, a call for companionship on a pilgrimage to God. And it means "going" from what was before, as we find in the Responsorial Psalm (which is truly a response to the first reading's invitation): "I rejoiced when they said to me, 'Let us go to God's house'."
But there is another "coming" in the Gospel, and it demonstrates what the Catechism says: that "God goes in search of man." When the centurion (representative of Isaiah's "many peoples") approaches Jesus to tell of his suffering servant, Jesus responds with an offer and a promise: "I will come and cure him."
All these comings and goings, both on the part of the "many nations" and on the part of God in Jesus, are the heart of Advent.