St. Teresa of Avila wrote that the Lord places in the soul the knowledge that He wants it to have and this without words or image. In this way, Teresa says, God gives the soul understanding of His desires and great mysteries and truths, or gives her understanding of some vision that He had given her [The Book of Her Life, Ch 27:6].
She wrote: "The soul undergoes a change ... it seems that a new, living high degree of love is beginning. For although the intellectual vision ... that represents God in an imageless way is more perfect, a wonderful thing happens when so divine a presence is represented in the imagination ... These two kinds of vision almost always come together. This is the way they occur: with the eyes of the soul we see the excellence, beauty, and glory of the most holy humanity; and through the intellectual vision . . . we are given understanding of how God is powerful, that He can do all things, that He commands all and governs all, and that His love permeates all things" [The Book of Her Life, C
The saints describe this light in two ways, the light of the glory of God that they see in a physial way through a vision, and then their mind is given infused knowledge of an explanation of what they have seen.
I had an experience of this: In California at my parish, we would have a Catechism study. Our priest was with us and we would cover about two pages in the two hours that we met. We had a couple of sceptics in the group which made our sessions interesting as we all learned, as we all took turns answering their questions. One day Father couldn't be with us and the sceptic challenged us with the statement that she didn't believe that the bread and wine changed into the body and blood of Jesus. As the rest gave their explanations, I remained silent, for I realized that I didn't believe it either.
That night when I went to bed I prayed, "Lord, I believe it because that is what I have been taught all my life by my Catholic faith. I believe it because I believe the stories of Eucharistic miracles that have taken place. But, Lord, I don't believe it. Please remove my unbelief."
During the night I awoke and there was a box of light around me. I thought, "This is interesting. Lord, I do not know what this means, but You are the potter, I am the clay. Mold me, meld me," and I went back to sleep.
The next morning I had forgotten the incident of the light and got dressed, ate breakfast, and was heading across the living room floor to go to the computer when I stopped in the middle of the room. I realized in a flash that I was a changed person! I believed! My whole being believed that the bread and wine became the body and blood of Jesus Christ when the words of Consecration were said over them. No argument convinced me of this - yet I believed! When the Church teaches about the light of infused knowledge given to us by the light of the Holy Spirit, I know exactly what it means by that statement. That knowledge, that belief was infused into my soul, not through words, but through Light.
I was a changed person! I truly believed this experience was from God. Going to Church was no longer a matter of Sunday obligation. Going to daily Mass became a treasured Grace. I believed everything I had been taught about the Eucharist. I could no longer day dream through the Mass. What was going on at the altar became very important. My presence, my total awareness, was now necessary. My Lord was right there! He was my food, my drink, my nourishment, the healing power within me. He was the source of all Grace I would need until I was able to receive Him again.
Kathy Moore, Song of Hope, (Coyote Publishing, Yreka, CA) p. 92 (available from this website).
Teresa of Avila, The Book of Her Life, trans. Kieran Kavanaugh and Otilio Rodriguez (Washington DC: ICS Publications, 1976).