A Compendium of Information and Images Of and Related to Christian Art and Iconography
The dove is a common representation of the seven gifts of the Holy Spirit. The seven gifts are:
Wisdom
Understanding
Counsel
Fortitude
Knowledge
Piety
The Fear of the Lord
The Holy Trinity consists of the Holy Father, the Holy Son, and the Holy Spirit. As one third of the Trinity, the Holy Spirit is represented in various ways throughout history. Here on the left we see an image of the Holy Spirit as child floating at sea and on the right an image of the Holy Spirit as a dove emblazoned on a standard.
The Holy Spirit is here depicted on the right as a wizened old man who holds a crucifix in his hands. Note the dove resting above Christ's fallen head.