The church alone was meant to represent heaven on earth, but with the windows it seemed moreso. Radiant light was meant to be a physical manifestation of God, so the stained glass windows were meant to strike the attendees with the sense that they were transported to heaven within the church. Abbot Suger wanted people to move from thinking about the light to thinking about God.
Allowing the outside in may have been in line with all of the natural motifs the carvers used to show the importance of understanding nature as part of the universe God created for us.
The windows may have also been a hip new way to teach the masses the bible. It may have been like any of our newer tech advancements that schools use to get kids interested in learning. The light shining through the rose windows seems a lot like the light shining through an electronic device.