Advent, as I'm sure you are well aware, means 'coming.' There are three 'comings' of Christ that we recognize during this Liturgical season. Cistercian monk and (recently deceased) spiritual writer Thomas Keating writes, "The first is his historical coming in human weakness and the manifestation of his divinity to the world; the second is his spiritual coming in our inmost being through the liturgical celebration of the Christmas-Epiphany Mystery; the third is his final coming at the end of time in his glorified humanity."
In other words, there is a past, present, and future coming. The past is the memorial-aspect of Christ's coming 2,000 years ago. The future is the apocalyptic-aspect when he will come again at the end of time to bring the earth to final glory. The present is the grace-aspect of our Lord into our hearts right now.
A good image for Advent, particularly the "present" coming, is light. By the way, the major liturgical seasons of the year each have an attribution. Advent/Christmas/Epiphany is light; Lent/Easter/Ascension is life; Pentecost/Ordinary Time is love.
Light is pretty obvious for this present season. We have Christmas lights and, of course, the candles on the Advent wreath. The rose-colored candle we light this Sunday, being Gaudete Sunday when we rejoice looking ahead to Christmas.