《礼记·聘义》
聘礼的含义：爵为上公的诸侯，派卿出聘用七个介；爵为侯伯的诸侯，派卿出聘用五个介；爵为子男的诸侯，派卿出聘用三个介。这是为了表明贵贱。
聘礼，上公七介，侯、伯五介，子、男三介，所以明贵贱也。
The meaning of the betrothal gift: a vassal who is the upper duke, send a qing to marry with seven介; a vassal who is a marquis or earl, send a qing to marry with five介; a vassal who is a son or male, send a qing to marry with three介. This is to show the dignity and inferiority.