Thirty is a number which may be regarded, according to its connection, as 5x6 or as 3x10.
Responsible man imperfect in his ways with his fellow men would be suggested by the former, and so a few 30's appear together in the book of Judges. Jair the Gileadite (ch. 10:4) had 30 sons on 30 ass colts, having 30 cities: men acting, but only in a partial authority, not over all Israel. Ibzan also had 30 sons and 30 daughters (ch. 12:9). Abdon (ch. 12:14) had 30 nephews, besides 40 sons (Judg. 14:11). Thirty companions were brought to Samson, etc. In Ch. 20:39, and also in v. 31, Benjamin slew each time about 30 of Israel.
1 Sam. 9:22 shows about 30 persons bidden to the feast by Samuel.
David had 30 chief men, one of whom brought 30 with him (1 Chron. 11:42).
Ebedmelech took 30 men with him to release the prophet from his dungeon (Jer. 38:10).
David was 30 years old when he began to reign, in 2 Sam. 5:4. Joseph was 30 when he stood before Pharaoh. Both are types of our Lord, who began to be about 30 years of age (Luke 3:23) when He entered upon His public ministry. Here probably 3x10 will be clearly seen: Divine perfection in full responsibility before God.
Yet Judas covenanted to betray Him for 30 pieces of silver (Matt. 26:15) even as Zechariah in his prophecy (Ch. 11:12) says, "they weighed for my price thirty pieces of silver." Connect with this the price of a gored servant 30 shekels in Ex. 21:32.
The mourning for Aaron was 30 days (Num. 20:29). Also, for Moses (Deut. 34:8).
Noah's ark was 30 cubits high (Gen. 6:15) and so was the "holy" of Solomon's temple (1 Kings 6:2).
Ezra brought back 30 chargers of gold, and 30 basins of gold (Ezra 1:9,10).
Solomon's laver was 30 cubits in circumference (1 Kings 7:23).
Esther says (Ch. 4:11) she had not been called to go in to the king for 30 days. And in Dan. 6:12, it was for 30 days forbidden to make any petition to God or man.
(These chief uses of the number are noted for the purpose of further consideration and so with others of the numerals, where the precise value is not seen clearly.)