This was a cover - which you know if you read Wicked Guilty Pleasures today...
It was also, bar none, the biggest hit ever up until that time, spending ten weeks at the top of the Billboard charts in 1977 (a feat matched by this song in 1980 and not eclipsed until 1993). It came to be when Joseph Brooks, the songwriter, became disillusioned for one reason (some say he was the Harvey Weinstein of his day) or another with the original vocalist, and had Debby Boone rerecord it - in a more Christian reading of the love song.
None of Brooks' ugliness is Debby's fault. She did a beautiful job singing this in her own right.