The threefold mission of Satan is to steal, kill and destroy (Jn 10:10). This mission is the only reason why Satan can be found anywhere. His going to and fro the earth (Job 1:7) is for one reason: to fulfil this mission in the lives of  as many people as he can reach and deceive. Satan brings death. Jesus brings life. Satan “set his heart against Job” (Youngs Literal). The question God had asked Satan in Job 1:8, was not an invitation for him to attack Job. No, it was rather an exposure of Satan’s attitude towards Job. Satan was already thinking of how to harm Job. Notice that he did not express ignorance of whom God was talking. He even reminded God of the protective hedge with which He had surrounded Job and all that he had. God’s blessing upon a man or woman attracts Satan’s hostility towards him or her. Satan hates to see any human being surrounded with God’s goodness and prosperity. That was why he schemed to steal, kill and destroy Adam and Eve. Before the Fall, Adam and Eve fulfilled 3 Jn vs 2: they prospered in all things and were in health even as their souls prospered (Job 1:10).
       The Bible does not mince words in telling us that we have an enemy. It should not surprise us that we are Satan’s enemies. There are basically two kingdoms in existence on earth: the kingdom of God (represented by light) and the kingdom of Satan (represented by darkness). These kingdoms are diametrically opposed to each other. Consequently, belonging to either of them automatically makes you either an active or a passive enemy of the other. The Bible says, “We know that we are of God, and the whole world lies under the sway of the wicked one.” (1Jn 5:19). The fact that we who are of God live in a world that lies under the sway of the devil, makes us targets of his attacks. Jesus warned His disciples of the impending hostilities they were to face: “If you were of the world, the world would love its own. Yet because you are not of the world, but I chose you out of the world, therefore the world hates you.” (Jn 15:19). According to Jesus, the hatred of the world for us results from its hatred for Him. As the ruler of this world (Jn 14:30), Satan will not tolerate the invasion of his territory. Therefore, for Christians—who are the light of the world—to live in his domain is threat to his kingdom (which darkness symbolizes).
    It is mainly for this reason that the Bible uses the language of warfare to describe the Christian life. Such expressions as, “…cast out demons…” (Matt 10:8), “… trample on serpents and scorpions, and over all the power of the enemy…” (Lk 10:19), “… we do not war according to the flesh. For the weapons of our warfare are not carnal but mighty in God for pulling down strongholds,” (2Cor 10:3-4), “Put on the whole armor of God, that you may be able to stand against the wiles of the devil.” (Eph 6:11), “Fight the good fight of faith…” (1Tim 6:12), etc all point to the fact that we are involved in a spiritual  military conflict. It is, therefore, important for us to pay attention to the dynamics of the war we are fighting so as to know who our enemies really are, their weapons and strategies. As Christians, we cannot afford to be ignorant of our involvement in spiritual warfare and neither should we stand aloof. There is no neutral place. You are either for one kingdom or against it. Shalom.