Those not regenerated by the Holy Spirit cannot resist the devil, since they do not have the power to overcome him. Therefore he holds them in the darkness of ignorance and error, and casts them into the abyss of various vices.
"The whole world lies in evil," that is, all people except those regenerated by the Spirit of God in holy baptism are in the realm of the devil. They are strangers to the gifts of grace, or strangers to the grace-filled Kingdom of Christ.
Jesus Christ Himself revealed this truth to Nicodemus, saying: "Truly, truly, I say to you, unless one is born of water and the Spirit, he cannot enter the Kingdom of God" (Jn 3:5).
Why can he not enter? Here is the reason: "That which is born of the flesh is flesh." That is, one born of sinful man is likewise a sinner, incapable of entering the Kingdom of God or of being a member of the grace-filled Kingdom of Christ, His Church.
"And that which is born of the Spirit is spirit" (Jn 3:6). The one regenerated by the Spirit becomes spiritual, obeys the Spirit, acts according to the inspiration of the Spirit, and is perfected with the Spirit's cooperation.
In the Lord's conversation with Nicodemus, "flesh" means the same thing as "world" in the Theologian.