Sometimes we get so familiar with some readings that we end up just "reading the words" instead of earnestly proclaiming "God's word." It can happen with readings that are repeated yearly, such as with the Christmas season or Ash Wednesday.
If we get so familiar with a reading where we feel we've "got it" and no longer need to study it, we risk proclaiming from the top of our heads instead of the depth of our hearts, and hinder the chance for God's word to touch our listeners.
Thomas Merton in his powerful book, Opening the Bible, said it all in these words...
There is, in a word, nothing comfortable about the Bible...until we manage to get so used to it that we make it comfortable for ourselves. But then we are perhaps too used to it and too at home with it. Let us not be too sure we know the Bible just because we have learned not to be astonished at it, just because we have learned not to have problems with it. Have we ceased to question the book and be questioned by it? Have we ceased to fight it? Then perhaps our reading is no longer serious.
Over the years, each time I prepare for a reading I've done before, I always seem to discover something new. The more I dig and the more commentaries I consult, the more freshness I can carry up to the ambo and avoid giving listeners that "same ol' same ol'" delivery.
So stay fresh! Your fellow parishioners will thank you for it... if not directly, at least in their hearts.