Hello and welcome to just answer Jeep. There is a problem with your clutch. It is not releasing and that is why you cannot shift into a gear with the engine running. Either something has broken in the clutch such as a pressure plate, or release fork, or it may be a hydraulic problem with the clutch master or slave cylinder. It may even be a seized pilot bearing in the end of the crank shaft. In either case, the trans will need to be pulled and the clutch system inspected and repaired/replaced.
Wish I had a quick fix for you but you will need to disassemble the clutch to check this out. If you have a fair amount of miles on the Wrangler, then plan on redoing the whole clutch system (disc,pressure plate,throw out bearing, and flywheel resurfacing)
Hope this information helps, and let me know if you need more assistance with this.