Why do we need to believe Jesus Christ?

When we are considering God, why did He create us, or when we need Divine Help, or what is Eternal Life, or is Heaven real? We are dealing with a dimension we do not know much about. That is why there are so many religions, each giving their interpretations. 

God has to send someone who is from Heaven to tell us what Heaven is like and the correct reality of the Spirit, and about life after death. 

No one has seen God at any time. The only begotten Son, who is in the bosom of the Father, He has declared Him.
— John 1:18 KJV
If I have told you earthly things, and you do not believe, how shall you believe, if I tell you of heavenly things? 13 And no man has ascended up to heaven, but he that came down from heaven, even the Son of man which is in heaven.
— John 3:12 KJV

God has decided that the only person who has the Authority to communicate to us about Him, is His Son. 

For there is one God, and one mediator between God and men, the man Christ Jesus;
— 1Timothy 2:5 KJV