advent is a time of asceticism

Yes, Advent is a time of asceticism. The latter originally meant “training.” The liturgical color violet should remind us of that, but also the practice of our Orthodox brethren to fast during this time. When we practice asceticism we stop treating things as ends for us and begin to accept God’s order again. We retrain ourselves, so to say; fasting is just one aspect of that retraining. True asceticism is a tool to prepare ourselves, to be open to receive the Word Incarnate, and goes beyond a mere giving up of some objects (alcohol, chocolate, etc.) but aims to recalibrate our entire focus towards reality. It aims at changing our desire, to turn it away from selfishness and toward the attitude of acknowledging God’s order, receiving it in obedience.
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Wisely, the mystics remind us that such phases of giving up things are to be interrupted by phases of fulfillment, of action, like our breathing is a harmony of inhaling and exhaling. When we inhale, we fill our lungs with the oxygen we need. For that purpose, however, we have to be open: If our airways are blocked, we cannot inhale. We cannot do so in a vacuum, either, and the world around us is just that: an empty place that cannot (ful)fill us. Inhaling, however, is rather passive; we are filled with something. Asceticism works a bit like this. It removes blockages and directs us to sources of fresh air. It prepares us to be (ful)filled. Only when we exhale do we become truly active. We use the air stored in us to speak, to sing, for bodily action—we express ourselves. We come to ourselves and to the mystery of our own being, God, and meet him in our soul.

Here.