LORD, now lettest thou thy servant depart in peace: according to thy word.
For mine eyes have seen: thy salvation,
Which thou hast prepared: before the face of all people;
To be a light to lighten the Gentiles: and to be the glory of thy people Israel.
Glory be to the Father, and to the Son: and to the Holy Ghost;
As it was in the beginning, is now, and ever shall be: world without end. Amen.
The Book of Common Prayer, 1662
Simeon was a servant of God who had been promised by God that he would not die without "seeing the salvation" that God would bring about physically through the person of Jesus Christ. This canticle is the record of Simeon's praise following the encounter with the infant Jesus. So why do we sing it now? Because in Biblical theology, ["This IS my body . . . this IS my blood] we in the bread and wine have also made an encounter with the physical Christ; we have "seen the salvation" of God--we have tasted, touched and handled it. We, too, must praise God!
It always amazes me how these truths are "hidden" in the liturgy for us to dig out.
"A light to lighten the Gentiles . . . the glory of thy people, Israel." How wide, how inclusive, God's grace.