Bieber reportedly held up a copy of The Meaning of Marriage: Facing the Complexities of Commitment With the Wisdom of God as he revealed Wednesday: "You got good days and you got bad days. It's not real if it doesn't have any bad days."
The "No Brainer" singer seemed in a better mood as he danced and talked to fans outside Baldwin's apartment building, TMZ reports.
The couple were spotted getting emotional during a bike ride in New York on Tuesday. Bieber and Baldwin comforted each other as they both appeared to cry in each other's shoulders.
Written by New York Times bestselling author Timothy Keller with his wife Kathy Keller, The Meaning of Marriage is a guide to "what marriage should be according to the Bible." The book's description says it "is essential reading for anyone who wants to know God and love more deeply in this life."
Bieber proposed to Baldwin in the Bahamas on July 8. The two had reconnected shortly after Bieber split with longtime on-again, off-again girlfriend Selena Gomez after previously dating 2015 to 2016.
A source told Us Weekly in July that the 24-year-old singer "needed" the engagement.
"He has been a kid sensation for as long as he can remember," the insider explained. "You become muted to that fame. He finally feels somewhat normal and it's a right time for him to settle down with one person."
At the time, another source close to the model said the two were planning "a very small wedding," noting that they wanted the event to be "private, intimate."
Some fans are still clinging to the theory that the two have already gotten married in a secret ceremony, without announcing it to the public. The theory began when Baldwin wore a new ring on a date with Bieber last week.
Fans noticed a diamond eternity band on Baldwin's left ring finger, while her engagement ring was nowhere in sight. The band was accompanied by a thicker gold ring, and fans thought it was a sign that the two had tied the knot in secret.
Fans point to their shared passion for the Christian faith as further evidence. Baldwin's father, Stephen, works as a minister in various Born-Again Christian organizations, and Bieber reportedly asked for his permission before proposing to Hailey. Bieber himself has put an increasing emphasis on religion in recent years, and the couple attends church together on a regular basis.
Baldwin's original engagement ring was made by Jack Solow, an esteemed private jeweler in New York City's Solow & Co.