The Kingdom of God/Heaven is the first and central message Jesus Himself preached, and the only message He commissioned His disciples and later His first apostles to preach proving that this message of the Kingdom was not intended to be part of the Christian message of Salvation but the very foundation of it.
From that time Jesus began to preach, and to say, Repent:for the kingdom of heaven is at hand
Matthew 4:17 KJV
And Jesus went about all Galilee, teaching in their synagogues, and preaching the gospel of the kingdom, and healing all manner of sickness and all manner of disease among the people.
Matthew 4:23 KJV
For too long, the Body of Christ has been taught that God's desire was only to get them to heaven when in fact it wasn't that at all, but rather to get Heaven to you.
God's plan of salvation starts with belief in Jesus Christ as being the Son of God who was sent to proclaim and demonstrate the Person, Presence, and Power of God to humanity, and ultimately go on to vicariously atone for the sins of humanity by His death, and then finally provide us not only with forgiveness of sin through His Blood, but freedom from sin and it's power through the Person of the Holy Spirit whom He would send to those that believe on Him who then takes us from leads us and guides us into all truth, and transforms us from glory to glory into the image and likeness of Christ, then becoming like Him we learn to surrender our own will for the Fathers, which causes the Kingdom of God (the rule and reign of God) to come in the earth!
9After this manner therefore pray ye: Our Father which art in heaven, Hallowed be thy name. 10Thy kingdom come, Thy will be done in earth, as it is in heaven.