The idea, most common to Gnosticism but also present in most Western Mystical Traditions such as Kabbalah and Sufism that each human being contains within himself a portion of God, or in other terms that our soul is at least partially created in the Image of God.
In these theologies, the purpose of life is to enable the Divine Spark to be released from its captivity in matter and reestablish its connection with or simply return to God who is perceived as being the source of the Divine Light. In the Gnostic Christian tradition (e.g. the Valentinian Church, the Cathars, the modern Lectorium Rosicrucianum etc.) Christ is seen as an Avatar of the Light which has taken human form in order to lead humanity back to the Light. The Cathars in particular saw this idea expressed most powerfully in the opening words of the Gospel of St John