Heaven on Earth
There is a difference between the Kingdom of Heaven and the Kingdom of God. The Kingdom of Heaven is (for all intents and purposes) a physical place. It is an external place. On the other hand, the Kingdom of God is less corporeal so to speak. It is an internal place.
The Kingdom of Heaven is the place souls go. It is where God and the angels reside. The Kingdom of God is an idea, or more specifically, an ideal. Something we should strive to create.
In Luke 17:21 Jesus says, "...the Kingdom of God is within you". (KJV) Other translations say "among" or "in the midst" of you. In the Gnostic Gospel of Thomas, it is within and without.
People tend to think of Christianity as an external religion. We worship an external God. Depending on denomination, we say take these sacraments, make confession, observe these days, these rituals, thede times, this diet. In essence, "do". But Christ says the kingdom is within. It is a state of being. In other words, "Be ye holy, for I am holy". (1 Peter 1:16) You contain the Kingdom of God, but you also are the Kingdom of God. In this way, Christianity becomes an internal religion. Our redemption comes in being rather than doing. Many people do good works but are not good people. Matthew 7:21-23 tells us that we should do what God asks, but that not everyone who prophesies or casts out devils in the Lord's name will see Heaven. They must hear and do, but also be.
The other translations of "...the Kingdom of God is 'among' you" or "'in the midst' of you" also offer insights into the nature of the Kingdom of God. Not only do we house God's Kingdom, but we also have the power to create it wherever we go. In our gatherings (church, family, or any other gathering), the Kingdom of God is made "in the midst" of us. "Where two or three are gathered together in my name, there am I in the midst of them." (Matthew 18:20) By our gatherings with each other, we have created a sacred place where the Kingdom of God can reside on earth.