Pastor means shepherd. Through the church, Christ calls pastors to shepherd souls by preaching, teaching, administering sacraments, leading public worship, praying, counseling, and reaching the lost. The New Testament mentions several such men, including Epaphras; in fact, three books of the Bible (1 Timothy, 2 Timothy, and Titus) were written to explain their responsibilities.
In the OPC, pastors are ministers of the Word. (Ministers can also function as evangelists or teachers.) They are carefully trained and tested. Sometimes ministers are called teaching elders because their shepherding responsibilities overlap with those of the other elders, as seen in 1 Timothy 5:17.
We sometimes call our elders ruling elders to distinguish them from ministers of the Word (who are also known as teaching elders). Together, the ruling and teaching elders comprise the session of a local church, and are responsible for its governance and spiritual leadership.
The office of elder carries both weighty responsibility and high honor. In Acts 20:28, Paul exhorts the elders of the church in Ephesus: “Pay careful attention to yourselves and to all the flock, in which the Holy Spirit has made you overseers, to care for the church of God, which he obtained with his own blood.”
The word deacon comes from the Greek diakonos, meaning servant. Under the supervision of the session, deacons manage church resources as stewards, and serve the needy as agents of Christ’s mercy. We find their origins and responsibilities in Acts 6:1-6 and their qualifications in 1 Timothy 3:8-13.
See XI. Deacons in the OPC Form of Government for more detail.