The song of songs, which is Solomon's.
Song of Solomon 1:1
"Solomon wrote Shir Hashshirim, or “Song of Songs,” probably near the beginning of his reign, around 965 B.C. Using poetical language befitting of the flourishing time period in which it is set, the king appears to be writing of his own love... Written in the style of idyl poetry, the Song of Solomon’s theme is the king’s love for a girl from the
country. For a king, love, not political gain, would motivate this type of marriage. Scholars have long credited the book with a deeper meaning illustrating Christ’s love for the church and its individual members. Both OT and NT illustrations portray God as an ardent lover and His people as His bride. While this allegorical application may be found, we must not overlook the book’s practical application for relationships today.
What Romans is to righteousness by faith, Song of Solomon is to romantic love. Significantly, the couple remains as enthralled with each other in the twilight of their relationship as in the beginning. This image contrasts sharply with the low expectation we have of marriage today. We think it’s normal for the excitement to fizzle. On the contrary; the faithful Christian lover will cherish his beloved just as much, and find just as much excitement and pleasure in her, after thirty years of marriage as after thirty seconds." BibleUniverse