Jesus answered and said to him, Most assuredly, I say to you, unless one is born again, he cannot see the kingdom of God. That which is born of the flesh is flesh, and that which is born of the Spirit is spirit. (John 3:3, 6)
When a person is born again, their spirit is made alive, even though it had previously been dead for their entire life. That person's spirit is simultaneously united with God's Spirit as one. We then know God personally in the Spirit, not in the flesh, because God is spirit. We see Him, hear Him, and know Him in and by the Spirit.
The spiritual realm is unseen, unlike the material world. The spiritual, the things that are not seen, are eternal. Everything you see in the material universe will one day be gone.
These things I speak to you are spirit and they are truth. If you are not born again, you cannot discern them because you are not in the spirit but in the flesh. No one can see God unless they are born again, born of the Spirit of God.
Nicodemus said to Him, How can a man be born when he is old? Can he enter a second time into his mother's womb and be born? Jesus answered, Most assuredly, I say to you, unless one is born of water and the Spirit, he cannot enter the kingdom of God. That which is born of the flesh is flesh, and that which is born of the Spirit is spirit. (John 3:4-6)
"Do not marvel that I said to you, 'You must be born again.' (John 3:7)
Being saved is an idiom for being born again and filled with the Holy Spirit. What are we being saved from? All people have fallen short of the glory of God and are sinners. God is perfect and we are not. Because of His perfect justice, sin must be punished. The wages of sin is death. But God loves the world so much, He became a man and died for the sins of the world. The eternal Son of God was born of a virgin. He is Jesus of Nazareth. Jesus lived a sinless life, the God-man, the Son of God, completely obedient to God the Father. He then willingly went to the cross, despising the shame of it, and took the sin of the world upon Himself.
He willingly laid His life down and went to the cross because of the joy of knowing that because of the cross, anyone that loves Him and believes in Him will have eternal life, and not spend eternity separated from God because of their sin.
How can our sin be laid on Him and His righteousness be imputed to us? The biblical answer is, "not by good works, but by faith." Only the grace of God can give us the free gift of forgiveness through Jesus Christ, and eternal life in Him.
Sincerely repent (turn from) your sin today, and truly believe in the Lord Jesus Christ in your heart, and you will be saved, born of God. To know God and enter Heaven, all must be born again, born of the Spirit, united to God through faith in Christ. Turn from your sin and ask Him into your heart today.