Like so many great innovations in football, the Texas concept was born out of desperation. The Packers would face Tony Dungy's Tampa Bay Bucs twice a year and the Tampa 2 was a tough nut to crack. Eventually, Holmgren came up with the Texas concept. If the defense was going to drop their linebacker deep to the middle of the field, Holmgren would take advantage of the room underneath in the middle.
This is it. This is the concept. It's a two man, high-low game. The tight end pushes upfield - on a post route, in this case - while the running back runs an angle route.