This is one of those things that may be difficult to grasp because technically God is spirit and has the capacity to be everywhere at once. He is not limited to space-time as you and I are. He is an unlimited being, yet he has limited himself for our sake. Heaven is his abode. The place where he resides, but if we know our Old Testament we know that God created Heaven and Earth together (Gen.1:1). He used to walk on the Earth with Adam and Eve in a paradise known as the Garden of Eden. But when Adam and Eve sinned against God they were expelled from the Garden and the presence of God.
Our sin has caused God to separate himself from us. The world that God created and blessed has become infected with sin. Darkness cannot exist in the presence of light and so too sin cannot exist in the full presence of God. Moses spoke with God face-to-face, but in a limited way (Ex 33:11) . Much like the world experienced when Jesus became a man and took on flesh (Phil 2:6-7). When Moses asked to see God in all His glory, God said it couldn’t be done without killing Moses (Ex 33:20, John 1:18, 1 John 4:12). So in a sense what we see and experience of God is a veiled experience. We have yet to fully experience Him. Hold on, we will. There will be a new Heaven and a new Earth and God himself will be the shining light. Sin will be dealt with once and for all and we will all be in the full presence of God (Rev. 21:23, 22:3-5, IS. 60:19-22). Until that time there is a separation. We pray to God in Heaven because Heaven has yet to come down to earth.
Think of it this way. In WWII the Germans advanced on France and took it fairly quickly. France was under German occupation. However, there were still several men and women, boys and girls who operated as the French resistance. Resisting the German occupation and working to get information to the Allies. They had a vision of seeing their country liberated. The reality was that their country was overrun by Germany and so they were living in a German state, but they took bold risks and sacrificed everything to see their liberty restored.
Earth is a seized state. It has been given over the prince of the power of the air, aka Satan or the Devil (Eph 2:1-2, Mat 4:8-9). But Christ has come to liberate us from the tyranny of sin. Once we have been set free, we still live among a sinful people. Christ has given us the mission to share the good news of liberation with the world. The Earth will become a truly free state once again.
Our Prayers now are offered up as a message from behind enemy lines. They help to focus us in on the mission. They line us up with where God is working. They empower us to see a better day. They give us opportunity to offer hope. It’s a phone call to the liberating force. We don’t have the power to free ourselves, but we know who does.
We come to God in prayer simply, relationally, in community, and with a view toward Heaven. This is completely different than how the Pharisee/ hypocrites of the day were praying. They were praying profoundly, non-relationally, in a fashion designed to show that they were superior to others and for personal benefit. Their prayers weren’t heard by God because they never fully intended them to be.