'Thirty' has a twofold significance because it is is the product of five and six, and also three and ten. From five multiplied by six, it signifies some aspect of combat, because 'five' signifies some part or aspect, and 'six,' combat. From three multiplied by ten, it signifies something full of remains of good and truth, because 'three' signifies fullness, and 'ten,' remains of good and truth. A composite number involves the same as the simple numbers it has as its factors.

(Reference: 2 Samuel 5:4; Arcana Coelestia 5335; Luke 3, 3:23, 23; Numbers 4:3, 4:23, 4:30)