15. first-fruits of Achaia—the first Achæan converts (compare Ro 16:5). The image is from the first-fruits offered to the Lord (Le 23:10; compare 1Co 15:20). The members of this family had been baptized by Paul himself (1Co 1:16).
addicted themselves to the ministry of the saints—Translate, "Set themselves, (that is, voluntarily) to minister unto the saints" (compare 2Co 8:4).