There are three Gospel Canticles, so called because they are drawn from the Gospels (each from Luke), and they all reflect on the arrival of the Savior in their own particular ways. The Benedictus is the first of these in liturgical order (though second in order of biblical appearance), was first uttered from the mouth of Zechariah, and dwells especially on the pre-gospel work of God in the birth of John the Baptist. Luke 1:67 introduces this canticle as a prophecy; these words are the words of God spoken forth to his people both in that birthday celebration and ever since in the Scriptures.
In the birth of John, the Baptist, the Forerunner, we are invited to see the accomplished work of God: “he has come to his people and set them free.” The canticle then explores this proclamation in two parts, examining the soon-to-born Christ for five verses (in the Prayer Book’s versification), and examining the ministry of John for the last four. In anticipating the advent of the Christ, Zechariah focuses mainly on the fulfillment of God’s earlier promises and to raise up a mighty savior. He remembers his covenent, he keeps his oath, just as the Old Testament prophets had pleaded for God to do, and this culminates in the attainment of perfect freedom to worship God without fear, “holy and righteous in his sight all the days of our life.” This is salvation, particularly the telos or end-goal of salvation. This emphasis on the previously-known Word of God is fitting, as John would go on to be a minister of the Word in a very forceful sense, his preaching vividly lining up with the old prophets some four centuries earlier. Thus the canticle moves on to focus on baby John himself, elucidating his future ministry. He will be a prophet, the forerunner of Christ, preaching the forgiveness of sins unto salvation. Through that ministry, “the dawn from on high shall break upon us” and many will be guided out of darkness and the shadow of death into the way of peace.
So when we pray this canticle every dawn, in daily Morning Prayer, we awaken anew to the saving work of God in Jesus Christ, and the light of his Word both in the old Prophets and in the New Testament, or Covenant, wrought by Christ our Lord. This canticle grounds us in the Gospel.