"Rainbow" symbolizes the spiritual Covenant, the Testament of God to the peoples of His Commandments, revealed by Him from the beginning of the creation of Man to the present time. 

 "Rainbow" is a symbol of the totality, versatility and completeness of the spiritual "Light" revealed by God - the Truth, the Wisdom of His Will, spiritually illuminating the "Earth", i.e. enlightening the peoples; the Truth, which was originally expressed by the Patriarchs, Prophets, Jesus Christ and Apostles in the Holy Scriptures.

"Rainbow" is a symbol of harmony, of the fusion of "Heaven", i.e. the spiritual height of the Truth of God's Will with "Earth", i.e. the peoples who fulfill it.