Satan, the lower case "god of this world", has the power to keep lost souls from discovering the Light, God's love for humanity, the truth (Christ crucified for our sins), the only means by which to escape his every snare. Satan thought he was victorious at the cross, but learned later that it was his defeat (1 Cor 2:8). He is desperate to keep this truth hidden from all and, by the sovereignty of God, has been given the ability to do so. Consider his beguiling of Eve in the garden (2 Cor 11:3) and also his persecution over Job (Job 1:7-12).
2 Corinthians 4:4
In whom the god of this world hath blinded the minds of them which believe not, lest the light of the glorious gospel of Christ, who is the image of God, should shine unto them.
Ephesians 6:10-18
Finally, my brethren, be strong in the Lord, and in the power of his might. 11 Put on the whole armour of God, that ye may be able to stand against the wiles of the devil. 12 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. 13 Wherefore take unto you the whole armour of God, that ye may be able to withstand in the evil day, and having done all, to stand. 14 Stand therefore, having your loins girt about with truth, and having on the breastplate of righteousness; 15 And your feet shod with the preparation of the gospel of peace; 16 Above all, taking the shield of faith, wherewith ye shall be able to quench all the fiery darts of the wicked. 17 And take the helmet of salvation, and the sword of the Spirit, which is the word of God: 18 Praying always with all prayer and supplication in the Spirit, and watching thereunto with all perseverance and supplication for all saints;