(from 1 to 13), theological symbols:
(1) The Unity of God.
(2) The hypostatic union of Christ, both God and man.
(3) The Trinity.
(4) The number of the Evangelists.
(5) The wounds of the Redecmer: two in the hands, two in the feet, one in the side.
(6) The creative week.
(7) The gifts of the Holy Ghost (Rev i. 12). Seven times Christ spoke on the cross.
(8) The number of the beatitudes (Matt. v. 3-11).
(9) The nine orders of angels (q.v.).
(10) The number of the Commandments.
(11) The number of the apostles who remained faithful.
(12) The original college.
(13) The final number after the conversion of Paul.
Odd Numbers. “Numero Deus impare gaudet” (Virgil: Eclogues, viii. 75). Three indicates the “beginning, middle, and end.” The Godhead has three persons; so in classic mythology Hecate had threefold power; Jove's symbol was a triple thunderbolt, Neptune's a sea-trident, Pluto's a three-headed dog; the Fates were three, the Furies three, the Graces three, the Horae three; the Muses three-times-three. There are seven notes, nine planets, nine orders of angels, seven days a week, thirteen lunar months, or 365 days a year, etc., five senses, five fingers on the hand and toes on the foot, five vowels five continents, etc. etc. A volume might be filled with illustrations of the saying that “the gods delight in odd numbers.” (See Odd, Nine.)
To consult the Book of Numbers is to call for a division of the House, or to put a question to the vote. (Parliamentary wit.)
Pythagoras looked on numbers as influential principles.
1 is Unity, and represents Deity, which has no parts.
2 is Diversity, and therefore disorder. The principle of strife and all evil.
3 is Perfect Harmony, or the union of unity and diversity.
4 is Perfection. It is the first square (2 2 = 4).
5 is the prevailing number in Nature and Art.
6 is Justice (Perfect Harmony being 3, which multiplied by Trinity = 6).
7 is the climacteric number in all diseases. Called the Medical Number (2 syl.). 2. The Romans dedicated the second month to Pluto, and the second day of the month to the Manes. They believed it to be the most fatal number of all.
4 and 6 are omitted, not being prime numbers; 4 is the multiple of 2, and 6 is the multiple of 3.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894