Set me as a seal upon thine heart, as a seal upon thine arm: for love is strong as death; jealousy is cruel as the grave: the coals thereof are coals of fire, which hath a most vehement flame.
Seal - having her name or likeness engraven on it. His holy priesthood also in heaven, (Hebrews 4:14; "His heart" there answering to "thine heart" here, and "two shoulders" to "arm." Compare Jeremiah 22:24 with Haggai 2:23. The Church is sealed by the Holy Spirit (Ephesians 1:13-14). As in Song of Solomon 8:5 she was "leaning" on Him-i.e, her arm on His arm, her head on His bosom-so she prays now that her impression may be engraven both on His heart and His arm, answering to His love and His power (Psalms 77:15; see Isaiah 62:3). The prayer of the literal Zion here is answered in Isaiah 49:16, "Behold, I have graven thee upon the palms of my hands."
Love is strong as death - (Romans 8:35-39.) This their love unto death flows from His love unto death (John 10:15; John 15:13).
Jealousy ... the grave - zealous love, jealous of all that would come between the soul and Jesus Christ Psalms 106:30-31; Luke 9:60; Luke 14:26).
Cruel - Hebrew, quasha: rather, unyielding, hard: as the grave will not let go those whom it once holds (John 10:28).
A most vehement flame - literature, the fire-flame of Yah or Yahweh (Isaiah 6:6). Nowhere else is God's name found in the Song. The zeal that burnt in Jesus Christ kindled in His followers (Romans 15:30).