First, every pastor should already be doing the work of every believer. That is, he or she should be making disciples, loving one another, serving, and above all, keeping a growing relationship with God. Second, it would be reasonable to examine the Apostles' practices and assume that many of those things could also be the task of a pastor. Jesus told Peter, "Feed my sheep" and it seems that this could extent even to the pastor today. All of these things are seen repeatedly throughout the Bible.
But what does the Bible specifically say for the pastor? What instructions are available? to answer these questions, the Greek words presbytersos, episkopos, poimēn, kērux, or didaskalos are where a study like this should focus. These are the words that translate to elder, overseer, shepherd, preacher, and teacher, respectively. For the sake of this post, the uses and instruction to the overseer or episkopos will be examined. This is the word that is most often translated in English as bishop, pastor, or overseer.
In Acts chapter 20, Paul shows some concern that some wolves may slip into the church and teach false doctrine. He encourages the leaders to "pay careful attention" to themselves and to the "flock which the Holy Spirit has made [them] overseers" (Acts 20:28, ESV). He further encourages them to remain alert for those who would do harm to the church. And in this task of protector and caregiver to the church they must give much to the Church, just as Paul did.
Philippians is addressed to the saints, overseers, and deacons. This letter provides lots of instruction, especially that they would grow and mature in love and knowledge. In 1 Timothy, Paul provides of list of attributes and characteristics to examine when looking for an overseer for the church. But among this list he provides two clues about what the pastor seems to be expected to do. He says in 1 Timothy 3:2, that the overseer should be "able to teach" and in 1 Timothy 3:4-5 he writes, "He must manage his own household well, with all dignity keeping his children submissive, for if someone does not know how to manage his own household, how will he care for God’s church?" (ESV). It would seem from this question, that the pastor is to care for the church in like manner to caring well for his household.
And finally, in Titus 1:9, Paul says of the overseer, "He must hold firm to the trustworthy word as taught, so that he may be able to give instruction in sound doctrine and also to rebuke those who contradict it" (ESV).
Based on this instruction as well as the others, it would seem that the primary duty of the overseer is to teach sound doctrine and protect the flock from those who may try to teach otherwise. The teacher must also be the protector. And while the pastor is many things, these are the instructions specifically given to the overseer.