The title, pastor, is of Old Testament origin (as is preacher and elder). The only reference to pastors by name in the New Testament is in Ephesians 4:11 (showing that Paul did use the word), which states, "And he gave some, apostles; and some, prophets; and some, evangelists; and some, pastors and teachers." I will not go through the arguments about possible meanings in this verse, but it is obvious that the pastor is a New Testament office. But what does a pastor do?
Since the pastor's duties are not defined in the one New Testament verse that uses the word, we must look at other evidence. The most obvious evidence would be the definition of the word. A pastor is defined (even in my English dictionary) as a shepherd. He is one who looks after the sheep. In Jeremiah 10:21, the pastors are condemned because they have disobeyed the Lord and "all their flocks shall be scattered." Jeremiah 23:1 states, "Woe be unto the pastors that destroy and scatter the sheep of my pasture! saith the LORD." The next verse demonstrates that it is their job to "feed my [God's] people." Clearly, shepherds are those who keep, care for, and protect the sheep. In the Old Testament, the application is made to the leaders of the people of Israel. But what is a New Testament pastor?
We know that the position of a pastor is a New Testament office (Ephesians 4:11). We also know that a pastor is one who acts as a shepherd in caring for and feeding the sheep. All we need now is to find a New Testament office that has as its duties the caring for and feeding of the sheep and we will have identified the pastor. Again, the scriptures are clear. In 1 Peter 5:1-4, Peter gives an exhortation to the elders (v.1). He reminds them: "Feed the flock of God which is among you" (v.2). He also instructs them to be "ensamples to the flock" (v.3). Then, he reminds them of their responsibility to "the chief Shepherd" (v.4). The chief Shepherd is obviously Jesus Christ. By simply logic, we understand that those who care for the flock under the supervision of the chief Shepherd are under-shepherds. And, since a pastor is a shepherd, we can identify a pastor as an elder.
This proof can be duplicated in the sermon of Paul in Acts 20. In this chapter, Paul calls the Ephesians elders together (Acts 20:17) and gives them special instructions. His instructions include Acts 20:28-29 - "Take heed therefore unto yourselves, and to all the flock, over the which the Holy Ghost hath made you overseers, to feed the church of God, which he hath purchased with his own blood. For I know this, that after my departing shall grievous wolves enter in among you, not sparing the flock." What do we call someone who oversees a flock? He is a shepherd. And, what is another name for a shepherd? A pastor. Yet, in this passage, Paul is speaking to the elders. Therefore, we know that the elders are pastors.
As to the epistles of Timothy and Titus, they are called pastoral because they give special instructions to two young men who were themselves ruling over churches and who were also setting up bishops (another word for a pastor) and deacons over the churches. They deal with young pastors who were establishing and training other pastors. So, why have Bible students called these pastoral epistles instead of something else? Well, you check it out. How would it sound to call them bishoply or bishopful epistles? Or, perhaps we could have called them elderly epistles or elderal epistles. You see, pastoral, meaning that which concerns shepherds and their work, was already a word. It was only natural to apply this word to the epistles of Timothy and Titus. The other titles would certainly have been awkward.