"Let all things be done decently and in order." (1 Cor. 14:40 KJV)
The word liturgy means "order of worship." It comes from a Greek word meaning "public work," especially as rendered in a religious service. All churches have a liturgy. Some have thought more about what an "order of worship" should be than others have. In all cases, an order of worship guides us as to how we are to do the public work of giving God the glory that is due to his name.
Those in the Reformed and Presbyterian tradition see the order of worship as a dialogue between God and man. Isaiah 6:1ff. provides the pattern for this understanding. God is present and he is praised. The prophet humbles himself and pleads for forgiveness of his sins. God graciously grants forgiveness. Then God speaks to Isaiah, giving him his commission as a prophet. Isaiah responds in faith and obedience. Those are the essential elements of all worshippersonal, family, and corporate.
In our "liturgy" (order of worship), note that the dialogue pattern is the reason for the specific elements and their order. God speaks and we respond in praise and confession. We ask God to bless us in this particular service. We minister to one another and confess our sins. God promises us forgiveness by his word. We respond in thanksgiving and giving! (We give out of thanks for God's goodness to us.) We hear God's word read and ask for the Spirit's work to prepare us as it is preached. In preaching, Christ himself speaks to us by his minister who opens the Word of God faithfully. We respond in faith, obedience, and appropriate praise. We go forth with the promise of God's blessing.
What a privilege it is to have God speak to us through his minister. And what a privilege it is for us to respond to him as a congregation (not just individually or as a family). Prepare yourself for your holy dialogue with God through your worship service.