Genesis 3:14-15 And the Lord God said unto the serpent, Because thou hast done this, thou art cursed above all cattle, and above every beast of the field; upon thy belly shalt thou go, and dust shalt thou eat all the days of thy life: And I will put enmity between thee and the woman, and between thy seed and her seed; it shall bruise thy head, and thou shalt bruise his heel.

The serpent, that old snake, the dragon, the devil, Satan himself is the first one lost. He is cast out from the presence of God but because he is an Archangel, one of the named, an eternal creation, Satan cannot die a physical death. In this sense being lost means no longer being in the presence of God, in paradise. Then came Adam and Eve into the world, cast out of paradise, into this same world into which Satan was cast. Since we were created to be loved, and to love, being lost is losing that intimate relationship with God.

Ephesians 2:2 Wherein in time past ye walked according to the course of this world, according to the prince of the power of the air, the spirit that now worketh in the children of disobedience:

Skipping forward here a little, we find Satan once again in the description, the prince of the power of the air. Note carefully the influence of this prince of darkness as he influences mankind in his realm. Now quickly refer back to the opening verse and look at one particular word, enmity. Its meaning here is hostility, hatred, Satan hates all mankind. Another word associated with hostility is war. We will find another word soon associated with these thoughts called rebellion.

Ephesians 6:11-12 Put on the whole armour of God, that ye may be able to stand against the wiles of the devil. For we wrestle not against flesh and blood, but against principalities, against powers, against the rulers of the darkness of this world, against spiritual wickedness in high places.

Armour (armor) is used in warfare.