Her Nazarites were purer than snow, they were whiter than milk, they were more ruddy in body than rubies, their polishing was of sapphire:

Wesley's Notes

4:7 Nazarites - Her Nazarites in this place signify her separated ones, who either in respect of birth, education, estate, or place of magistracy, were distinguished from the rest of the people.

Jamieson-Fausset-Brown Bible Commentary

7. Nazarites-literally, "separated ones" (Nu 6:2). They were held once in the highest estimation, but now they are degraded. God's blessing formerly caused their body not to be the less fair and ruddy for their abstinence from strong drink. Compare the similar case of Daniel, &c. (Da 1:8-15). Also David (1Sa 16:12; 17:42). Type of Messiah (So 5:10).

rubies-Gesenius translates, "corals," from a Hebrew root, "to divide into branches," from the branching form of corals.

polishing-They were like exquisitely cut and polished sapphires. The "sapphires" may represent the blue veins of a healthy person.

Cheth.

Matthew Henry's Concise Commentary

4:1-12 What a change is here! Sin tarnishes the beauty of the most exalted powers and the most excellent gifts; but that gold, tried in the fire, which Christ bestows, never will be taken from us; its outward appearance may be dimmed, but its real value can never be changed. The horrors of the siege and destruction of Jerusalem are again described. Beholding the sad consequences of sin in the church of old, let us seriously consider to what the same causes may justly bring down the church now. But, Lord, though we have gone from thee in rebellion, yet turn to us, and turn our hearts to thee, that we may fear thy name. Come to us, bless us with awakening, converting, renewing, confirming grace.