it is all about intentions and what comes to pass from those intentions,as well as what is in your heart at the time to further explain what I mean it is written if I am not mistaking in either the books of kings or books of samuel or both,of an act that David did that was out of lusting desire and resulted in a man's death,the woman's name was bath-sheba and though David already had plenty of wives and concubines he looked upon her and lusted for her and put her husband at the front lines speaking of him as a valiant warrior and thought nothing of this until after the man died and he took proper steps to wait until bath-Sheba was no longer mourning and still thought nothing on what happened to Bath-Sheba's husband until a prophet came unto him telling of a man who had one ewe lamb and a man whom had many lambs and yet the man with many lambs thought to take the man with one ewe lamb's ewe lamb and the many with many lambs killed the man whom had only the one ewe lamb,and David himself said that it is was wrong that the man with many lambs killed the man and took his only ewe lamb,and the prophet said "thou art the man",and David rent his clothes and knew now what he had done and that God held him accountable for the man's death for he was the leader over the men on the battlefield and sought bath-sheba as his own and through this desire he killed her husband,that he didn't do this physically himself was of no difference to God,so basically what I'm getting at with this is that,anyone can kill in their heart without lifting a weapon,obedience is very important to God but he must have your heart as well,for if it is filled with hate,lust,or envy then you will do wrong by him,also to answer why we are to "love" our enemies is because "God does not delight in anyone's death"so a "True" warrior/soldier must know the difference between killing to protect their country and killing because they hate their enemy,a"True" warrior/soldier must not allow himself to be blinded by pride or hate,they are to have an unclouded mind,is it a sin to kill Yes it is,is it wrong to protect by killing when necessary,No,but most important one must stick to the goal all in their ranks are fighting toward otherwise a "warrior/soldier could jeopardize the overall mission,and speaking of battle in I believe matthew it is written"there shall be wars and rumors of wars but these things have to happen" so as much as many would like to see war done away with, it still continues because it is apart of God's plan,so will their still be a need of blood shed at times unfortunately yes,and it is sin no matter the cause but this is why we have grace now so that when there are times that require killing or blood shed that there is still salvation through Jesus and that is all the more a great blessing all in all,for if not for Jesus dieing for us then how much more difficult would it be to keep doing right for God,or worse die in our sins before even lifting a weapon,Jesus died so as that all would no longer die to the law but be able to live without condemnation unto death,for now if their be times that unfortunately require blood shed we are allowed to do so,but only for a "justifiable cause" not for any form of "vengeance" "for "vengeance is mine saith the lord" nor for any form of self gain just as I described before.