Why has Christ commanded us to address God as “Our Father”?
That immediately in the very beginning of our prayer He might awaken in us a childlike reverence for and confidence in God which are the foundation of our prayer, namely that God has become our Father in Christ and will much less deny us what we ask of Him in true faith than our parents will refuse us earthly things.
Scripture references
Why are the words “in heaven” added?
So that we do not form earthly conceptions of God’s heavenly majesty, and so that we expect from His almighty power everything necessary for soul and body.