A work done for one's satisfaction or for the benefit of someone you love, not for money or rewards

Henry - a famous writer - wrote a book about his town, but he didn't make any money out of it because it was a labor of love for his beloved town

Enrico, famoso scrittore, ha redatto un libro sulla sua città, ma non ci ha guadagnato una lira: lo ha fatto gratis et amore Dei per la sua amata città

Of biblical origin, the phrase appears twice in the New Testament of King James' Version of the Bible (1611): Hebrews 6:10 and Thessalonians 1:3. It refers to those who do God's work as a labor of love.