01 Wj 4.7 V8 engine knocking

I have recently moved down to Savannah Georgia for college. It was 2 and a half hour drive for my jeep which has about 139,000 on it. I drove down here no problem and drive for a few days, and let the jeep sit for about 2 days, and when I started it up, the engine has a bad knocking sound. I'm terrified to drive it, so if anyone coukd diagnose this, that'd be great. Thanks!

Update: replacing engine

The 4.7 doesn't handle abuse too well. It's nowhere near as bulletproof as the 4.0 or 5.2 engines were. My idiot stepson just threw a rod in his Dakota because he never checked the oil and barely even changed it the whole time he had the truck.
Now, this noise you're hearing, does it sound like it's a rod knock or lifter clatter? How many miles?
When you replace the engine you have to make sure the cam sprockets on the new motor are the same as the one you're pulling out. I think there was a change in 2003 with those sprockets and it will drive you nuts trying to figure out why the new engine runs so shitty because you have the wrong sprockets. Good luck, git it running soon!