"Joseph, son of David, do not fear to take Mary your wife, for that which is conceived in her is of the Holy Spirit; she will bear a son, and you shall call his name Jesus, for he will save his people from their sins."
Again, the words "do not fear" appear in the advent story. First, to Mary, now, to Joseph. Joseph's dream is a dream of courage, of moving beyond fear. It is a dream to act courageously and to banish fear.
How does one do that? Banish fear? To not fear? Can that willfully be done? Or does one just act despite the throes of fear?
I have been afraid, and I don't think that I could willfully throw off fear. But I have acted despite fear, and in the midst of acting, found that fear quietly fell away. The hardest part of acting when fearful is making that first move toward action while still afraid. Fear seems to be greatest just before the grand decision to act is made. Maybe that is what the angel is saying to Joseph.
Maybe the angel is telling Joseph to throw off fear by making a decision. And then, the angel tells him which decision to make and why. I imagine that once Joseph resolved to marry into God's future, his fear fell away and trust replaced it.