In this video from Life Teen, Joel Stepanek helps us understand the readings for the Fourth Sunday of Advent for Year A. These readings are about trust.
Ahaz puts his trust in other worldly powers instead of trusting in God. This is his downfall. Isaiah prophesies that a virgin will bear a son, and that son will be our savior. In the gospel, Joseph puts his trust in God. He listens to the message of the angel.