The topic for each Sunday will be published well in advance so that homilies at every Mass celebrated in the Diocese on that particular weekend will be on the same topic of Church doctrine/faith using the Catechism of the Catholic Church as a primary reference.
Catholic preaching in the last decades has moved away from sermons - topics chosen by the priest or preacher without any correlation to the lectionary readings. Priests were taught to preach homilies, which are specifically written to illustrate or complement one or more of the lectionary readings at the mass, frequently the gospel.
What exactly does catechetical preaching mean? Don't worry, it does not mean that homilies will become lectures. But a catechetical homily should teach or inform us about a particular aspect of the Catholic faith. Illustrative stories can still be helpful, but the gospel or the 1st reading may not specifically relate to the topic of the sermon. At daily mass, for example, if the priest preaches about the life of a saint, it could be a catechetical homily; we learn about the life of the saint, sometimes the controversies when the saint lived or the doctrines the saint might have taught or exemplified by his or her life.
The topics for these homilies are still being selected. Some of them might be grace, or original sin, or topics of belief in the Nicene Creed, etc. It's a noble experiment which I think will be well received.