What is the significance of church activities?

It depends or what you are really asking. The Liturgy of the Church is the "work of the People of God (those people God has called, note, they did not volunteer, they were called-- by God) to be his Priests,(hence, a Priestly People, not just clergy, but all the holy people of God, a people who "offer up" prayer and praise for the sake of the world), to be faithful witnesses of Christ in the world today." They do this because "on the night in which he was betrayed, Jesus took bread, blessed it and gave it to his disciples and said, 'take this and share it, for this is my body which is offered up for you. Do this in order to never forget me.'" And the same with the cup. They do this first because he said to do it and they trust he knows why he said do it, and secondly because it keeps in their minds how they are to live in this world-- by giving themselves to others as a gift and secondly to keep before them that they physically share the body of Christ in the world today. For all practical purposes, the Church is Christ in the world today, and here to serve the Father by spreading the news of the recreation of the the old order of the world, that is, that God rules. So, the work of the People of God is to serve the world in the name of God, just as Jesus once did, as God did, does. And to be a priestly people, offering prayer and praise for the sake of the world. One is called to this. Many volunteer and realize that it is not their joy, and leave thinking they have failed or that "church" does not "help them." Both responses are poor, for if you are called to serve, God's service is perfect freedom.