Historically, the banner is a symbol of victory and alludes to the Emperor Constantine, who , upon his conversion to Christianity, added the cross to his triumphant flag.

In Christian art, particularly in that of the Renaissance, the banner is used to symbolize Christ's victory over death through His Resurrection.

He is portayed carrying the banner as He arises from the grave, in His descent into hell, and in His several appearances
after His Resurrection and prior to His ascension.

In the design of this stained glass window, the victorious banner of the Resurrection is pictured surrounding and encompassing the cross, the symbol of death, suggesting the words of  Paul the Apostle in scripture...

"When the perishable puts on the imperishable, adn the mortal puts on immortality, then shall come to pass the saying that is written:

        Death is swallowed up in victory.
        O Death, where is thy victory?
        O Death, where is thy sting?

The sting of death is sin and the power of sin is the law. But thanks be to God, who gives the victory through our Lord Jesus Christ."

I Corinthians 15:54-56