The first and principal duty of a pastor is to feed the flock by diligent preaching of the word. It is a promise relating to the new testament, that God would give unto his church “pastors according to his own heart, which should feed them with knowledge and understanding” (Jer. 3:15). This is by teaching or preaching the word, and no otherwise. This feeding is of the essence of the office of a pastor, as unto the exercise of it; so that he who doth not, or can not, or will not feed the flock is no pastor, whatever outward call or work he may have in the church. The care of preaching the gospel was committed to Peter, and in him unto all true pastors of the church, under the name of “feeding” (John 21:15-17). According to the example of the apostles, they are to free themselves from all encumbrances, that they may give themselves wholly unto the word and prayer (Acts 6:1-4). Their work is “to labour in the word and doctrine (I Tim. 5:17); and thereby to “feed the flock over which the Holy Ghost hath made them overseers” (Acts 20:28): and it is that which is everywhere given them in charge.
This work and duty, therefore, as was said, is essential unto the office of a pastor. A man is a pastor unto them whom he feeds by pastoral teaching, and to no more; and he that doth not so feed is no pastor. Nor is it required only that he preach now and then at his leisure, but that he lay aside all other employments, though lawful, all other duties in the church, as unto such a constant attendance on them as would divert him from this work, that he give himself unto it—that he be in these things labouring to the utmost of his ability. Without this no man will be able to give a comfortable account of the pastoral office at the last day.
It is incumbent on [pastors] to preserve the truth or doctrine of the gospel received and professed in the church, and to defend it against all opposition. This is one principal end of the ministry, one principal means of the preservation of the faith once delivered unto the saints. This is committed in an especial manner unto the pastors of the churches, as the apostle frequently and emphatically repeats the charge of it unto Timothy, and in him unto all to whom the dispensation of the word is committed (I Tim. 1:3-4, 4:6-7, 16, 6:20; II Tim. 1:14, 2:25, 3:14-17). The same he giveth in charge unto the elders of the church of Ephesus (Acts 20:28-31). What he says of himself that the “glorious gospel of the blessed God was committed unto his trust” (I Tim. 1:11) is true of all pastors of churches, according to their measure and call; and they should all aim at the account which he gives of his ministry herein: “I have fought a good fight, I have finished my course, I have kept the faith” (II Tim. 4:7). The church is the “pillar and ground of the truth;” and it is so principally in its ministry. And the sinful neglect of this duty is that which was the cause of most of the pernicious heresies and errors that have infested and ruined the church. Those whose duty it was to preserve the doctrine of the gospel entire in the public profession of it have, many of them, “spoken perverse things, to draw away disciples after them.” Bishops, presbyters, public teachers, have been the ringleaders in heresies. Wherefore this duty, especially at this time, when the fundamental truths of the gospel are on all sides impugned, from all sorts of adversaries, is in an especial manner to be attended unto.
Sundry things are required hereunto; as—(1) A clear, sound, comprehensive knowledge of the entire doctrine of the gospel, attained by all means useful and commonly prescribed unto that end, especially by diligent study of the Scripture, with fervent prayer for illumination and understanding. Men cannot preserve that for others which they are ignorant of themselves. Truth may be lost by weakness as well as by wickedness. And the defect herein, in many, is deplorable. (2) Love of the truth which they have so learned and comprehended. Unless we look on truth as a pearl, as that which is valued at any rate, bought with any price, as that which is better than all the world, we shall not endeavour its preservation with that diligence which is required. Some are ready to part with truth at an easy rate, or to grow indifferent about it; whereof we have multitudes of examples in the days wherein we live. It were easy to give instances of sundry important evangelical truths, which our forefathers in the faith contended for with all earnestness, and were ready to seal with their blood, which are now utterly disregarded and opposed, by some who pretend to succeed them in their profession. If ministers have not a sense of that power of truth in their own souls, and a taste of its goodness, the discharge of this duty is not to be expected from them. (3) A conscientious care and fear of giving countenance or encouragement unto novel opinions, especially such as oppose any truth of whose power and efficacy experience hath been had among them that believe. Vain curiosity, boldness in conjectures, and readiness to vent their own conceits have caused no small trouble and damage unto the church. (4) Learning and ability of mind to discern and disprove the oppositions of the adversaries of the truth, and thereby to stop their mouths and convince gainsayers. (5) The solid confirmation of the most important truths of the gospel, and whereinto all others are resolved, in their teaching and ministry. Men may and do ofttimes prejudice, yea, betray the truth, by the weakness of their pleas for it. (6) A diligent watch over their own flocks against the craft of seducers from without, or the springing up of any hitter root of error among themselves. (7) A concurrent assistance with the elders and messengers of other churches with whom they are in communion, in the declaration of the faith which they all profess …
It is evident what learning, labour, study, pains, ability, and exercise of the rational faculties, are ordinarily required unto the right discharge of these duties; and where men may he useful to the church in other things, but are defective in these, it becomes them to walk and act both circumspectly and humbly, frequently desiring and adhering unto the advices of them whom God hath intrusted with more talents and greater abilities.
(John Owen, Works, vol. 16, pp. 74-75, 81-83).