Right from the early days of the Church, there was a clear need for divisions of labor. Acts 6:1-7 records an incident where some less-evangelical work was necessary, and the twelve apostles created a new group of workers, and delegated that task to them, so that the apostles could keep up their main evangelical work. This was an efficient, good distribution of work-- the apostles were most effective in reaching out to nonbelievers, so the care of the existing believers was handed out to others who could do that better.
As the quote from Romans 12 above notes, this is not just a one-time case from the early church, but a fact of life: people play different, specialized, roles in the Church, just as a human body has many specialized parts. Your liver has one purpose. Your backbone has another. Your heart a third. It would be insanity to expect your liver to try and keep you sitting or standing upright. It'd also be pretty darn stupid to try and put nutrients and/or toxins into your backbone and expect useful byproducts out. Trying to make your heart handle your sense of smell wouldn't work. Thus, anyone with even a passing familiarity with anatomy wouldn't expect body parts to be fully interchangeable.
The same is true, to a lesser degree, with the Church. Not everybody is a pastor. Not everybody is an extremely effective evangelist. Not everybody is a true servant. Not everybody is a prophet. Most of the time, you wouldn't want to pick someone out of the congregation at random at the start of the service and put them up in the pulpit to preach that week's sermon. A pastor with years of study and experience in public speaking will, nine times out of ten, give a better sermon. However, the flipside is probably true as well: nine times out of ten, the church's janitor can clean up better and faster than the pastor, due to experience.
There are some caveats to the dividing people into categories, however: humans can and do learn, especially when helped by God and the Holy Spirit. In small churches, the pastor might just be the janitor. And both the pastor and the janitor (when separate people) can evangelize others-- just as everyone in the congregation can do. Everyone in the church can and should pray. [1 Thessalonians 5:17] Everyone should be reading their Bibles. Everyone should be worshiping God-- some will make a joyful noise, some will make a great song, and some will just make noise. Everyone should serve others. All of those basics can and should be practiced by everyone, even if you're not that great at them.
As noted by Jesus in the parable of the good Samaritan [Luke 10:25-37], if a clear and obvious need is presented to you, then you must do something about it. There are times when you may be the only one capable of doing something, or the only one who notices a problem. Guess what? Be helpful, or get help from someone more qualified to help. [The good Samaritan couldn't dial 911 on his cell phone and get professional medical help, so he was on the spot.] This doesn't mean you're personally responsible for fixing every problem you notice; reporting it to those who can do a better job and can do such a thing is usually sufficient.
Within the categories everyone can and should do, some naturally excel. Some will seem more effective in prayer than others, but everyone still needs to do it. Incompetence is not a valid excuse with God when we are commanded to do things-- we must try, and ask for help from God and other Christians when we're stretched out of our normal behaviors. Romans 12 and 1 Corinthians 12 both explain how the Holy Spirit gives gifts to people, in all sorts of categories. Some people may have a gift in only one area. Others more. This is purely a matter for God to decide, but everyone tends to have an area they're most effective in doing God's work.
If you're unsure what area your gift(s) may reside in, run down the lists of gifts in the Bible-- while not necessarily complete, that's a good starting point-- pray over them, and try out ministries that use them. Through work, you can figure out where you're most effective.
The Church is made up of people with many different gifts. You cannot have an effective church of only pastors. You cannot have an effective church of only a choir. You cannot have an effective church of only janitors. You cannot have an effective church of any other single part; everyone must work together.
Not every part of the body is glamorous-- the pastors and choir tend to get a lot of attention, and the janitor almost none. However, as Paul notes, the "weaker" parts are as, if not more important. No backbone in the Church? The pastor might be preaching a wishy-washy sermon full of pop culture references to a recent hit movie, instead of the truth of the Bible. No prayer in the Church? It may seem aimless as people never tried to get God's direction for their lives. No armor of God in the Church? [Ephesians 6:10-18] Most likely run over by Satan, or otherwise made ineffective for God.
Paul was correct: we must treat the parts the world might think of as less honorable with special honor, not looking down on them. When was the last time you thanked the janitors at your Church for a job well done, just as you might thank the pastor for a good sermon? When was the last time you paid equal attention to the attractive as well as unattractive people around you at Church? We must be supportive of every part of the Church's body, even if our worldly sides don't like that, or don't see the need for some people in the body. God sees everyone's true purpose, their necessity-- he calls them into the church for a reason. So, even if you don't see that reason, or don't care for them, reach out in love to them, just as Jesus loved them way before you ever could.