A soldier is a person that will fight for you and that will lay down their lives to fight for your cause. This can make a soldier quite the intimidating figure because they will be willing to fight for what they or another person might believe in just for the purposes of furthering that goal.
A dream of a dead soldier could mean a multitude of things. For one it could be coming about because you are a soldier and you are worried about what might happen to you if they take you out on the battlefield. If you happen to know a soldier or be really good friends with one, this could also be why you are dreaming of a dead soldier, you are worried about their safety. A warzone isn't exactly the safest place to spend your time when you are in the army. But on a more obscure note a dream of a dead soldier could also mean that you are through putting up a fight. You have tried your hardest and you were unable to conquer. You will find it quite difficult to go on with your life after this.
A dream that you are a dead soldier could mean that you feel like you have fought for a certain cause and you have exhausted yourself in pursuit of that goal. You feel like you are too far gone in that regard and you may not be able to complete this goal. Still however you fight on because you need to accomplish what it is you set out to do. Whether you complete your goal or not in the end, your resolve to do so was admirable. You did more than could be expected of most people and this is something to celebrate, not something to be concerned about.