We first of all ask for an "angel of peace"! Yet which angel of all the heavenly hosts does not love peace and work towards it?
This is why we need to pray with simplicity and humility. We need to be 'selfless' in our prayer. Just as a nightingale sings without anyone seeing, we need to give ourselves over to the worship of God in secret.
On the feast day of the Exaltation of the Holy Cross (September 14), the Gospel reading brings to our attention the awesome events surrounding Christ's crucifixion and death.