この曲の歌詞は口語訳聖書（1955年版）からくるのです。
特に、マタイによる福音書７章１３〜１４節

The lyrics of this song come from the Kogoyaku Bible (1955).
In particular, Matthew 7:13-14

https://jco.ibibles.net/101Matthew.htm#101-7

Note: The idea to use 狭い門 as a tentative Japanese title for this song is partly from auto-suggest from Motion app.