The One Big Happy in Thursday’s comics feed:
From OED3 (Nov. 2010), under labour ‘task’:
labour of love a task undertaken either for love of the work itself or out of love for a person, cause, etc.; work of this nature.
The fixed expression — which Ruthie has presumably not heard before and so has eggcornishly reshaped — is Biblical in origin and has been used allusively in names of books, songs, films, and the like.
Etymology from OED3:
with allusion to 1 Thessalonians 1:3 (see quot. 1535-1 and compare Hellenistic Greek τοῦ κόπου τῆς ἀγάπης ) and Hebrews 6:10 (see quot. 1535-2)
[1535 Bible (Coverdale) 1 Thess. i. 3 Youre worke in the faith, and youre laboure in loue.
1535 Bible (Coverdale) Heb. vi. 10 God is not vnrighteous, that he shulde forget youre worke and laboure of loue, which ye shewed in his name.]
First non-Biblical cite:
1592 R. Greene Philomela To Rdr. sig. A4, I com contrary to vow and promise once againe to the presse with a labour of loue which I hatched long ago.
The Biblical sources in the KJV:
1 Thessalonians: 1:2 We give thanks to God always for you all, making mention of you in our prayers; 1:3 Remembering without ceasing your work of faith, and labour of love, and patience of hope in our Lord Jesus Christ…
Hebrews 6:10: For God is not unrighteous to forget your work and labour of love, which you have shewed toward his name…
Then a small sample of labor of love in titles:
book: Moira Weigel, Labor of Love: The Invention of Dating (2016)
song: Bon Jovi, “Labor of Love”, from This House is Not for Sale (2016), which you can watch here
movie: Labor of Love … a 1998 Lifetime television film starring Marcia Gay Harden and David Marshall Grant … directed by Karen Arthur and written by Nina Shengold (Wikipedia link)