The Holy Spirit, which every human needs, unites with the human spirit that is in us. It is the impregnation of God-life, which makes us the begotten but not yet born children of God's Family - heirs, but not yet inheritors.
It is the spirit of understanding, imparting to the physical brain spiritual comprehension - the ability to really understand spiritual knowledge. It is the divine love of God placed within us. It is the faith of Christ - the same faith Jesus had - now given to us. It is also the spiritual power we need to help us turn from, resist, and overcome Satan's "get" way and turn to God's "give" way.
It is the power by which the few firstfruits now called may develop God's holy, righteous, and perfect character, which is God's purpose for having put humanity on the earth - that God may thus reproduce Himself.
When Adam chose to disobey God, he was cast out of the Garden of Eden and denied further access to the Holy Spirit and eternal life. He was spiritually kidnapped by Satan! Although the world would then be ruled by Satan for 6,000 years, God knew that this was the best way for humans to learn their lesson.
Those who are called prior to Christ's return must, with the power of God's Spirit, overcome Satan while he is still ruling. That is not easy, but it helps them to qualify for greater positions of responsibility in the Kingdom of God. Greater character is built when one has obstacles, such as the Devil's influence, to overcome.
Living in a world filled with sin also helps us learn to thoroughly hate sin (Psalm 97:10; 119:104). The results of selfishness and competition are painfully obvious to those God calls out of Satan's world.
After Christ returns and restrains Satan, a utopia will finally result that will reflect the benefits of God's way. The comparison with Satan's 6,000 years of rule will be spectacular!