Calvin commenting on 1 Thessalonians 5:12-13 states well the importance of hard work in pastoral ministry and what our work actually is.
In the first place, he says that they labor. From this it follows, that all idle bellies are excluded from the number of pastors. Farther, he expresses the kind of labor when he adds, those that admonish, or instruct, you. It is to no purpose, therefore, that any, that do not discharge the office of an instructor, glory in the name of pastors. …
Now, this work is the edification of the Church, the everlasting salvation of souls, the restoration of the world, and, in fine, the kingdom of God and Christ. The excellence and dignity of this work are inestimable: hence those whom God makes ministers in connection with so great a matter, ought to be held by us in great esteem.
(HT: Gentry Hill)