The key word is "must." Our Lord commanded us many things, but the only time He used "must" is in reference to being born again.
Certainly a command is a command, and the Lord's followers must do it. His teaching on the mountain, Matt. 5-7, is filled with commands, and He simply issues His commandments as any commander confident in his own authority will do it. That is, He simply says "do these things." There is no threatening, there is no cajoling. there is no justifying, but He simply says "do these things," as one might well expect from a good, holy, and benevolent Co-creator of the universe.
And yet Jesus said, "Ye must be born again." Being born again of the Spirit of God is of course that which separates the believer from the mere professor of faith in Christ. He or she that is born again is born again of the Spirit of God and thus indwelled by the Spirit of God.
So being born again is really believing Jesus died for my sins rather than simply professing it. Profession and faith go together. Thus it says in Romans 10:9-10,
That is thou shalt confess with thy mouth the Lord Jesus and shalt believe in thine heart that God hath raised him from the dead, thou shalt be saved. For with the heart man believeth unto righteousness; and with the mouth confession is made unto salvation.
Many in the churches are perishing out of reliance on their confession on Sunday morning, even while they have no true confession by which we may know them as brethren in the Lord. Thus John 4;2-3 says,
Hereby know ye the Spirit of God: Every spirit that confesseth that Jesus Christ is come in the flesh is of God: and every spirit that confesseth not that Jesus Christ is come in the flesh is not of God: and this is that spirit of antichrist, whereof ye have heard that it should come: and even now already is it in the world.
I fear many who profess faith in Christ are perishing, because they have not been born again. These have put their faith in their confession rather than in Christ. Far better is it to put our faith in Christ and confess it!