"...Who art in heaven, hallowed be thy Name..."
There are other gods. Jesus said in His Sermon on the Mount, "For where your treasure is, there your heart will be also." (Matthew 6:21) Anything, be it good or bad, that draws our focus, our concentration, our total submission away from "Our Father", is our god, our idol. Before we can express our gratitude to Our Father be keeping the Ten Commandments, the first of those Commandments must be obeyed: a commitment to worship only the Lord.
When Jesus teaches us to pray Our Father "who art in heaven," He is showing us that we must recognize initially Who our Father is. He is not part of the creation. He is not part of this world. He is beyond human comprehension. This is the Father that we worship and pray to-not any other god or idol that is finite and created. He is greater than the loftiest ideal we can imagine, because even that is created and an idol.
Therefore, "...who art in heaven..." is immediately followed by "...hallowed be thy Name..." "Hallowed" means to make or set apart as holy; sanctify; consecrate. "Hallowed", therefore, means made or set apart as being holy; highly venerated; unassailable; sacrosanct. In our prayers, Jesus teaches us to begin by remembering in Whose Presence we are coming. That it is He alone Who is worthy of our worship, devotion, total commitment and surrended. That before we can begin to petition for others and ourselves; before we can begin the work of the Kingdom; before anything, we must begin with the focused desire to know He that is in heaven, He that created the heavens and the earth, He that is alone holy and worthy of our worship and praise.