Revelation 21:10 says, “And he carried me [the apostle John] away in spirit onto a great and high mountain and showed me the holy city, Jerusalem, coming down out of heaven from God.” Because New Jerusalem is spiritual, we need to be in spirit (our human spirit indwelt by the Spirit) to see it.
God “has given to us of His Spirit” (1 John 4:13) to remain in us eternally. This is the fulfillment of the Lord’s promise in John 14:16-17, “And I will ask the Father, and He will give you another Comforter, that He may be with you forever, even the Spirit of reality…He abides with you and shall be in you.”
Unfortunately we too often live according to (or in) our natural life rather than according to the Spirit in our spirit. Thus, 1 Corinthians 2:14-15 contrasts the soulish man and the spiritual man. The soulish man has a natural living, a living centered in the soul. The spiritual man is one who denies himself (Matthew 16:24-25) and has a living centered in the mingled spirit. Because we are at risk of living as a soulish man, Ephesians 4:30 warns us, “do not grieve the Holy Spirit of God.” On the positive side Galatians 5:16 encourages us, “Walk by the Spirit and you shall by no means fulfill the lust of the flesh.” Since Romans 8:13 says “if you live according to the flesh” it is clear that this is still a danger for Christians.
First Corinthians 12:3b tells us that “no one can say, Jesus is Lord! except in the Holy Spirit.” To honestly declare “Jesus is Lord” or to cry out to Him “Lord Jesus,” puts us in Spirit. Acts 2:21 tells us that “everyone who calls on the name of the Lord shall be saved.” Our first time to call “Lord Jesus” brings us our initial and eternal salvation, including our spirit being born of the Spirit (John 3:6). Our continued calling brings us daily and practical salvation, including living in (according to) Spirit. Our calling is likened to breathing in Lamentations 3:55-56; just as breathing is lifelong, so our calling “Lord Jesus” should be lifelong. Such spiritual breathing keeps us in spirit where we can see, receive, and discern the spiritual things (1 Corinthians 2:14-15) including New Jerusalem.