Haggai, who wrote in 520 B.C., was a contemporary of Zechariah who wrote from 520 to 518.
New Testament References
Haggai is referenced or alluded to at least three times in the New Testament. The first verse of his book is referenced in Matthew 1:12, while the twenty-second verse of chapter 2 is alluded to in Matthew 24:7. Finally, Haggai 2:6 is reference in Hebrews 12:26.
[When Was the New Testament Written?]
Consider Your Ways!
The phrase "consider your ways" is an exhortation from the Lord for his people to reflect on what they were doing. It is found twice in the King James Version of this short book (Haggai 1:5, 7). The people are also called upon three more times to consider other events.
Consider now from this day and upward, from the four and twentieth day of the ninth month, even from the day that the foundation of the Lord's temple was laid, consider it (Haggai 2:18, see also verse 15).

Name Dropper
Haggai is one of eight Old Testament authors who is mentioned in a book he did not write. The prophet is mentioned twice in Ezra.
Then the prophets, Haggai the prophet, and Zechariah the son of Iddo, prophesied unto the Jews that were in Judah and Jerusalem in the name of the God of Israel, even unto them (Ezra 5:1).
And the elders of the Jews builded, and they prospered through the prophesying of Haggai the prophet and Zechariah the son of Iddo. And they builded, and finished it . . . (Ezra 6:14).
Jewish Tradition
The 1906 Jewish Encyclopedia states that Haggai was remembered as a singer of psalms. He was also considered the first to use the term "Hallelujah." The prophet, also according to the encyclopedia, is credited with the following.
[Who Wrote the Book of Psalms?]
"Among these were a provision for the intercalation of the month of Adar, a decision in favor of enlarging the altar, and a decision permitting the bringing of sacrifices independently of the existence or presence of the Temple . . .
"(He also is credited with) the organization of the priestly service into twenty-four relays and the regulation of the wood-contributions . . ." (article on Haggai).
How Many Came Back?
The 1911 Encyclopedia Britannica has the following tidbit of information regarding the number of Jewish captives who came back to Judah.
[Israel's Migration After Captivity]
"Thence, when the opportunity came under Cyrus (the Great), some 50,000 Jews, the spiritual heirs of the best elements of the old Israel, returned to found the new community." (article on Haggai).
Haggai was likely one of this huge group who were allowed to travel back to their homeland.
Another Name for Jesus
Haggai reveals a reference to Jesus Christ not found anywhere else in the Bible.
And I will shake all nations, and THE DESIRE OF ALL NATIONS shall come: and I will fill this house with glory, saith the Lord of hosts (Haggai 2:7).
Unmatched Accuracy!
The book of Haggai is arguably the most accurately dated book in the entire Bible! It offers precise clues regarding not only when it was written but also when certain events took place. The book opens by revealing when the prophet received his first message from God.
In the second year of Darius the king, in the sixth month, in the first day of the month, came the word of the Lord by Haggai the prophet . . . (Haggai 1:1).
Darius I the Great became ruler over the mighty Persian Empire in late September of 522 B.C. Haggai, along with the writers Jeremiah, Ezekiel and Zechariah, used dates based on the beginning of the religious year (Nisan / Abib 1) as opposed to the start of the civil year (Tishri 1), when it came to Hebrew / Babylonian / Persian kings (Mysterious Numbers of the Hebrew Kings).
The first day of the sixth Hebrew month in 520 B.C. was Elul 1. This corresponded to Sunday August 27.
The prophet's second message from God was received on the 24th day of the sixth month of the same year or Elul 24 (Haggai 1:15). This date was Tuesday September 19. The third message was given on the 21st day of the seventh month or Tishri 21 (2:1). This day, the last day of the Biblical Feast of Tabernacles, was Sunday October 15.
The prophet's last two messages were received on the 24th day of the ninth month or Kislev 24 in 520 B.C. (Haggai 2:10, 20). Interestingly, God confirms this date himself in verse 18 of chapter 2. This date was Sunday, December 17.
What is a Signet?
The last verse of Haggai refers to a signet that is mentioned only in nine other verses in the Bible.
In that day, saith the Lord of hosts, will I take thee, O Zerubbabel, my servant, the son of Shealtiel, saith the Lord, and will make thee as a signet . . . (Haggai 2:23).
[Does the Bible Forbid Jewelry?]
A signet was of great value in the world of the Old Testament. It was commonly possessed by princes, kings and others who possessed authority.
"The signet in Old Testament times was an engraved stone set in a gold or silver finger ring, bracelet, or armband . . . When pressed upon wax or soft clay, the ring left the impression of the personal insignia of the bearer . . .
"It symbolized status or position and the binding nature of the authority attached to items sealed by the ring" (Nelson's NKJV Study Bible).