Jeremiah 31:14 - Matthew Poole's English Annotations on the Holy Bible

By priests some understand the ministers of the gospel, whom God here promiseth liberally to provide for; or rather, by giving a success to their ministry, and letting them see the fruit of their labours, make to rejoice: in which metaphorical sense I should rather interpret it, applying it first to the priests of the Jews after the captivity, of whom it is said, Ezra 6:16, that they kept the feast of the dedication of the second temple with joy; and Ezra 6:22, the Lord had made the people joyful. Nor were the people for a short time only satisfied with the Lord's goodness. In a secondary typical sense it may also signify the spiritual success and rejoicing of good ministers under the gospel, and the spiritual joy of believers. This rejoicing is metaphorically expressed by fatness, with allusion to the rift of the sacrifices under the law. It is a usual thing for God by his prophets to express New Testament duties and privileges by phrases borrowed from the worship of God under the Old Testament. See Isaiah 66:22,23.