Jackson suffered a concussion in Week 6 when Atlanta Falcons CB Dunta Robinson flew into a defenseless Jackson. Robinson also suffered a concussion on the play and it's one of a few plays that has been at the forefront of the NFL's effort to eliminate illegal hits from the NFL.
The decision to sit Jackson was expected and makes sense. The Eagles have a Week 8 bye which means sitting Jackson now will give him nearly three weeks of rest between the Falcons game in Week 6 and the Eagles Week 9 game.
It's also possible that Jackson is out for multiple games but the Eagles have yet to address that.
Here is the DeSean Jackson concussion video.
Check out Bleeding Green Nation for more on Jackson.