I'm amazed at the number of times I've heard people ask why traction is such a big deal in the world of motorsports. Whether it's drag racing at over 100 MPH or rock crawling at under 5 MPH, traction is easily the most important consideration. Why? because nothing else means a thing if you can't get power to the ground when it matters.
There are a number of ways to get traction, and each one has its own advantages and disadvantages in different situations. There is one category that, while important in other fields, I will not discuss here; aerodynamics aren't a factor at 5 MPH. The rest, I'll address in the order they come into play, starting from the ground and working to the engine.
Your tires are (or at least, they should be) the only place your jeep touches the ground. If they aren't grabbing the ground, you aren't going anywhere. There are three major factors that should influence your choice of tires: footprint, rubber compound, and tread pattern.
Some people seem to think the entire purpose of a suspension lift is to allow for greater tire clearance. While lifts do increase the tire size you can run, there is something else that matters even more: flexibility. To put it another way, your tires won't do you any good if you can't keep them on the ground.
Getting the power of your engine out to the tires is a tricky thing. For maximum traction, you need the power going to all four of your tires. To do that, you'll need a four-wheel-drive with fully locking differentials.