At church, you must…

What must we do during church? Now before you get all high and mighty and give me this the-church-is-the-people speech, I’m talking about the church service. The gathering. The worship service. That time on Sundays that you meet with other believers. What must we do during this time?
There are two basic thoughts, which each have their own variations. The regulative principle adheres to the belief that God has ordained everything fit for public worship in Scripture–sola scriptura. Simplified, if it isn’t in Scripture, you can’t do it during church. The normative principle states that one can use whatever means they wish during church as long as it is not prohibited in Scripture.
Both of these principles are based on what you cannot do in church. But what must we do? This question includes two parts:
1) What does Scripture require? and
2) What is necessary to reach the unsaved?
So tell me. At the core of what you do, what is necessary?
