In Supernatural, the term Cherub simply refers to an angelic occupation inherent in cupids as it describes a lower order or choir of angels. According to Castiel, humans have misinterpreted the role of them. There are dozens of them stationed on Earth as of now, according to Castiel5.14 My Bloody Valentine In their occupation, they're responsible for marking humans making them fall in love on instruction from Heaven.
John and Mary Winchester fell in love because Michael had a Cherub intervene which ultimately resulted in their marriage; they also couldn't stand each other prior to a Cherubs intervention5.14 My Bloody Valentine
Cherub Angels In Lore
The information below is info derived from http://en.wikipedia.org/wiki/Cherub but I reworded and reorganized the information.
Cherubs or Cherubim are an order of angels that are of a lower ranking than Seraphs but they outclass all other angels of the angelic choir or spheres which divides, separates and fully compromises the angelic society.
Attributes of Cherub Source.
- They guard, watch and monitor God's throne room at all times.
- They have four different faces, each representing a different organism, and have four wings that are used for flight. Two of the wings extended upward, meeting above and sustaining the throne of God; while the other two stretched downward and covered the creatures themselves.
- God also stationed two Cherubs at the gate of the Garden of Eden.