“…on earth as it is in heaven…” While we might consider this from the trajectory of the revelation of the God to Israel preceding Jesus’ statement (which would be a fitting approach), we might also consider this statement as embodied in the one leading the prayer: Jesus the Christ. Such a reflection (drawing from the New Testament) offers several hearings of this text leading to praying and doing.
We might understand by “heaven” not an ethereal disembodied sphere of existence “out there” or even “above here”, but as wherever the kingdom of God is present. Wherever God reigns is most properly to be regarded as “heaven”. While God’s reign is not fully experienced “on earth” it is coming to bear “on earth” even as it has from the beginning of creation and the planting of the garden.
Considering such a view of “heaven” we might define “on earth” as that sphere of existence wherein God’s reign is less fully yet being realized.
There is a strange movement that occurs here. It is never as if “earth” is not where God reigns, nor is “heaven” to be regarded as itself such bliss that nothing more could be added to it. No. The kingdom of God is yet more realized in both heaven and earth by the two becoming the kingdom of our God and His Christ. This is not to suggest something essential lacking to the reign “in heaven,” but to appeal to the grace of God towards, in, and for us in his self-giving love embodied in Christ Jesus.
Christ Jesus brings heaven to bear on earth. Or more properly first, the Holy Spirit brings heaven to bear on earth in the virgin Mary. This is “God with us”. God being toward us, heaven toward earth (even in the earth).
Christ Jesus bears heaven on earth as the light burdens being given in place of earth’s heavy burdens. He seeks and saves that which is lost as a light blazing in the darkness. Earth cannot be regarded as wholly other to heaven. Unclean spirits are cast out. Disease and even death itself is demonstrably overcome on earth as it is in heaven. And these are all laid to bear on the cross as one raised up from the earth and lifted up into heaven in shamefulness. Yet the Father sees fit to not leave his Son buried in the earth, but raises him up to ascend into heaven to His right hand as King Jesus. And from there the Father pours out Jesus’ Spirit upon all flesh to fill the hearts and mouths of the saints with heaven on earth until the earth should be filled with the fullness of the glory of God.
And heaven shall be opened and the Christ descend bearing heaven to the earth. At last the kingdom shall come in fullness as his reign continues without end. His throne (the throne of God and of the Lamb) established in His city now come down from heaven and established upon the new heavens and the new earth. It is here, in the two joining, that we are praying toward as Jesus taught us to. It is here, in the two joining, that we are working toward as the Spirit compels and empowers us to. It is here that we (and all of creation with us) are moving toward: the day when the Father in heaven’s name is holified, His kingdom come, and His will done “on earth as it is in heaven”.