Seven

Boyd’s Bible Dictionary:

A favorite, and often symbolic, number among Hebrews
(Gen. 2:2; 7:2; 41:2-32And on the seventh day God ended his work which he had made; and he rested on the seventh day from all his work which he had made. (Genesis 2:2)
2Of every clean beast thou shalt take to thee by sevens, the male and his female: and of beasts that are not clean by two, the male and his female. (Genesis 7:2)
2And, behold, there came up out of the river seven well favored kine and fatfleshed; and they fed in a meadow. 3And, behold, seven other kine came up after them out of the river, ill favored and leanfleshed; and stood by the other kine upon the brink of the river. (Genesis 41:2‑3)
). Used as a round number (1 Sam. 2:55They that were full have hired out themselves for bread; and they that were hungry ceased: so that the barren hath born seven; and she that hath many children is waxed feeble. (1 Samuel 2:5); Matt. 12:4545Then goeth he, and taketh with himself seven other spirits more wicked than himself, and they enter in and dwell there: and the last state of that man is worse than the first. Even so shall it be also unto this wicked generation. (Matthew 12:45)). Type of abundance and completeness (Gen. 4:15,2415And the Lord said unto him, Therefore whosoever slayeth Cain, vengeance shall be taken on him sevenfold. And the Lord set a mark upon Cain, lest any finding him should kill him. (Genesis 4:15)
24If Cain shall be avenged sevenfold, truly Lamech seventy and sevenfold. (Genesis 4:24)
; Matt. 18:21-2221Then came Peter to him, and said, Lord, how oft shall my brother sin against me, and I forgive him? till seven times? 22Jesus saith unto him, I say not unto thee, Until seven times: but, Until seventy times seven. (Matthew 18:21‑22)). These references, and other places, show a seventh day and seventh year sabbath and a seven times seventh year of Jubilee; also sacrificial animals limited to seven, and the golden candlesticks. Seven priests with seven trumpets surrounded Jericho for seven days, and seven times on the seventh day. In the Apocalypse we find seven churches, seven candlesticks, seven stars, seven seals, seven trumpets, seven vials, seven plagues, seven angels.

Concise Bible Dictionary:

From Manners and Customs of the Bible:

The number seven is used frequently in Scripture, and expresses the idea of completeness or fullness. Thus the text represents the hypocrite as having a heart filled with abominations. This figurative use of the number seven obtains in some parts of the East at the present day. It is frequently employed to signify an indefinite number, but always a large number, and hence conveys the idea of sufficiency. The Scripture passages where the word “seven” is used are too numerous to be quoted here. They are scattered all through the Bible, especially in the prophetical books; the book of Revelation making most frequent symbolical use of the word.
The interesting question, Why the number seven should be regarded a perfect number? is one the discussion of which does not fall within the scope assigned to this work. Those who desire information on this subject, and also on the general question of the sacred numbers used in the Bible, may consult, in addition to the various Bible Dictionaries and Encyclopedias, Stuart on the Apocalypse, in his Introduction, § 7, “Numerosity of the Apocalypse,” vol. 1, p. 130 and in Excursus II, “On the Symbolical Use of Numbers in the Apocalypse,” vol. 2, p. 409. Dr. Whedon also has a very valuable and characteristic note on the same subject in his Commentary on the Gospels, vol. 2, p. 77.