Key into the ignition and hold it there and after a few seconds the engine started?

We own a 99 jeep grand cherokee limited. Once in a while it has a little problem like the ignition won't start right away though it shows all the lights but we can't hear the engine running at all so out of frustration one day I hold the key into the ignition and hold it there and after a few seconds the engine started. So obviously there is a delay when we start the car, it happens once in a while. But of the times it start just even if it is freezing outside, So what seems to be the problem?