1 Timothy 3:8

We have here the character of deacons: these had the care of the temporal concerns of the church, that is, the maintenance of the ministers and provision for the poor: they served tables, while the ministers or bishops gave themselves only to the ministry of the word and prayer, Act 6:2, Act 6:4. Of the institution of this office, with that which gave occasion to it, you have an account in Act 6:1-7. Now it was requisite that deacons should have a good character, because they were assistants to the ministers, appeared and acted publicly, and had a great trust reposed in them. They must be grave. Gravity becomes all Christians, but especially those who are in the office in the church. Not doubled-tongued; that will say one thing to one and another thing to another, according as their interests leads them: a double tongue comes from a double heart; flatterers and slanderers are double-tongued. Not given to much wine; for this is a great disparagement to any man, especially to a Christian, and one in office, unfits men for business, opens the door to many temptations. Not greedy of filthy lucre; this would especially be bad in the deacons, who were entrusted with the church's money, and, if they were covetous and greedy of filthy lucre, would be tempted to embezzle it, and convert that to their own use which was intended for the public service. Holding the mystery of faith in a pure conscience, Ti1 3:9.

— Matthew Henry's Concise Commentary (public domain)

The deacons were chosen by the voice of the people. CYPRIAN [Epistle, 2.5] says that good bishops never departed from the old custom of consulting the people. The deacons answer to the chazzan of the synagogue: the attendant ministers, or subordinate coadjutors of the presbyter (as Timothy himself was to Paul, Ti1 4:6; Plm 1:13; and John Mark, Act 13:5). Their duty was to read the Scriptures in the Church, to instruct the catechumens in Christian truths, to assist the presbyters at the sacraments, to receive oblations, and to preach and instruct. As the "chazzan" covered and uncovered the ark in the synagogue, containing the law, so the deacon in the ancient Church put the covering on the communion table. (See CHRYSOSTOM [19], Homily on Acts; THEOPHYLACT on Luke 19; and BALSAMAN on Canon 22, Council of Laodicea). The appointing of "the seven" in Act 6:1-7 is perhaps not meant to describe the first appointment of the deacons of the Church. At least the chazzan previously suggested the similar order of deacons. double-tongued--literally, "of double speech"; saying one thing to this person, and another to that person [THEODORET]. The extensive personal intercourse that deacons would have with the members of the Church might prove a temptation to such a fault. Others explain it, "Saying one thing, thinking another" (Pro 20:19; Gal 2:13). I prefer the former.

— Jamieson-Fausset-Brown Commentary (public domain)