This is a good question. I think that the #1 priority should be to glorify God in all that we do. Yes, this is broad, and it includes many things, but if we leave the glorify God part out, our purpose can become distorted. If we state that our #1 goal is to evangelize, then as human we will ultimately resort to evangelism that results in more harm than good. I think history proves that (crusades, inquisition, trying to "save the indians), and I think everyone has encountered some form of evangelism that has left us with a bad taste in our mouths. If we think that the first priority is to teach the word on sundays, and we leave out Glorifying God, then the church will become self serving and exclusive. We will no longer worry about serving others and ministering to our communities. This can go for just about any purpose of the Church: leave out glorifying God, and it becomes distorted and sinful.
 
I'm not saying that Evangelism, preaching, teaching, serving, and ministering are bad things; they are not. I'm saying that if they become our main goal, apart from glorifying God through our actions and words, the church can do more harm than good. This begs the question, how do we glorify God? Well, I think this lies with Jesus's statement that the greatest commandment is to love the Lord with all our heart, minds, soul, and strength, and our neighbors as ourselves. If we as Christians are loving God and neighbors the way that Christ demonstrated, then the word of Christ WILL go forth to all the nations. The church WILL teach scripture, take care of the poor and the widowed, and minister to the world in the way that it should. These actions flow from a heart that is seeking to love and glorify God.
 
Unfortunately, churches are made up of sinners, and we so often get caught up with things that are not of God. We forget that our ultimate purpose is to Glorify God, and we try to glorify ourselves instead. We focus and harp on nonessentials, and we alienate people because of our own sin. Thank goodness we have a saviour, because I for one know that I need him.
 
I'm sorry, I don't think I answered your question well, but I did the best I could. :)