Illumination is the act where God allows for the comprehension/understanding of God, God's will, or God's works. M.X. Seaman helpfully bifurcates the doctrine of illumination into two sub categories: Initial and Progressive. He terms the fusion of the two as transformative illumination. He defines it as such, “transformative illumination is that process whereby the Holy Spirit’s initial illumination enables his ministry of progressive illumination such that his work of transformation results in the life of the believer.”
In establishing a Trinitarian doctrine of illumination, it is necessary to appreciate the distinctions in the involvement of the different persons in the work of illuminating. The Father’s role in illumination is as the One who gives, drawing people to His Son.  The Father also allows for the blinding of mind. The Son’s role in illumination is as the instrument to creation; the light.  The Son also is the nexus between the Father and the Spirit’s illuminating work. The role of the Holy Spirit in illumination is of the agent that grants the understanding. Similar to the previously noted Trinitarian doctrine of inspiration,  the involvement of Trinitarian members in illumination may overlap and simultaneously feature distinctions.