If the battery is dead or near dead, your Jeep engine will not run... or at least it will not run well once the jumper battery has been disconnected. The alternator won't put out power without the battery being able to provide its required 12 volt "exciter voltage" so with a dead or nearly dead battery and an alternator incapable of putting out enough power, the ignition system will not be be able to produce enough spark.
So first, your battery could be old enough to finally be giving up the ghost. If it's not, then it just needs to be fully charged with an external battery charger. I would take it down to your local battery store and have them do what's called a "load test" which will test the battery's true condition. Then you'll know if it's truly bad or if it just needs a good charge.
Make sure too that both battery connections are clean and tight. Lastly, your Jeep is a Jeep, not a "car". Jeeps feel bad if you refer to them as a 'car'.