first most obvious, make sure the transfer case is not in neutral.
If the shifter is stuck in one position you can access the floor panel over the shifter, then remove the shifter, sometimes when worn or loose they can become stuck and you can fix it by lifting the shifter out of the trans.
Lastly, and you would probably already suspect this, the clutch is gone, but you would have had a lot of issues and slippage leading up to a complete failure.
The neutral safety switch keeps the starter from engaging when the transmission is in any gear EXCEPT park or neutral. A faulty switch would either allow the starter to engage any time or not allow the starter to engage at any time.
idler sensor!
Most likely a broken gear cluster
Bad transmission rebuilder
buy a Toyota
it's spelt 'litre'.
To remove the steering gear box from a CJ5 Jeep, start by disconnecting the battery and removing the steering column from the gear box. Next, detach the pitman arm using a puller if necessary, and then unbolt the gear box from the frame. Finally, carefully remove the gear box from its mounting location, ensuring you collect any washers or spacers. Always refer to the vehicle's service manual for specific instructions and torque specifications.
Gear oil...usually 75w90 weight. I would use Royal Purple or any synthetic gear oil. That goes for both differentials and the transfer case.
The tag on the back of the case has the part number, model number and gear ratio on it.
Stop the car, put it in 1st gear and dont change it, dont stop or put your clutch in for any reason.
Check the fluid. If full, take it to the trans shop.
You may need a new transmission, or you at least need to have that one rebuilt.