Canticle of Zachariah daily? Why?

Why is the Canticle of Zachariah is part of the daily morning prayer?

There is no one sure answer to this question. But it seems probably due to the first part of the canticle, as a song of thanksgiving for the coming of the Redeemer, that it finds an appropriate place in the office of the Church every morning at Lauds.

The Benedictus, given in Luke 1:68-79, is one of the three great canticles in the opening chapters of this Gospel, the other two being the Magnificat and Nunc dimittis. The Benedictus was the song of thanksgiving uttered by Zachary on the occasion of the birth of his son, St. John the Baptist. It is Jewish in form, but Christian in sentiment. The local colouring and nationalistic character of the first half are so noticeable that Loisy has conjectured that it existed previously as a simple psalm, which Zachary adapted, his additions being, he contends, easily discernible. (Revue d'hist. et de lit. relig., May-June, 1903, p. 289). There are, however, grave objections to this view, and an opposite theory has been put forth that the Benedictus was composed with special reference to the names of Elizabeth, Zachary, and John, for Elizabeth, Jusjurandum quod juravit; Zachary, Memorari (testamenti sui sancti); and John, Ad faciendam misericordiam.

The whole canticle naturally falls into two parts. The first (verses 68-75) is a song of thanksgiving for the realization of the Messianic hopes of the Jewish nation; but to such realization is given a characteristically Christian tone. As of old, in the family of David, there was power to defend the nation against their enemies, now again that of which they had been so long deprived, and for which they had been yearning, was to be restored to them, but in a higher and spiritual sense. The horn is a sign of power, and the "horn of salvation" signified the power of delivering or "a mighty deliverance". While the Jews had impatiently borne the yoke of the Romans, they had continually sighed for the time when the House of David was to be their deliverer. The deliverance was now at hand, and was pointed to by Zachary as the fulfilment of God's oath to Abraham; but the fulfilment is described as a deliverance not for the sake of worldly power, but that "we may serve him without fear, in holiness and justice all our days".

The second part of the canticle is an address by Zachary to his own son, who was to take so important a part in the scheme of the Redemption; for he was to be a prophet, and to preach the remission of sins before the coming or the Orient, or Dawn, from on high. The prophecy that he was to "go before the face of the Lord to prepare his ways" (v. 76) was of course an allusion to the well-known words of Isaias (40:3) which St. John himself afterwards applied to his own mission (John 1:23); and which all the three Synoptics adopt (Matthew 3:3; Mark 1:2; Luke 3:4). It is probably due to the first part of the canticle, as a song of thanksgiving for the coming of the Redeemer, that it finds an appropriate place in the office of the Church every morning at Lauds. It is believed to have been first introduced by St. Benedict (Beaume, I, 253). According to Durandus, the allusion to Christ's coming under the figure of the rising sun had also some influence on its adoption. It is also used in various other liturgical offices, notably at a funeral, at the moment of interment, when words of thanksgiving for the Redemption are specially in place as an expression of Christian hope. - The Benedictus (Canticle of Zachary)

The Canticle of Zachary (the Benedictus Deus, Luke 1:68-79) is said or sung at lauds ("morning prayer") because, as Abbé Nicolas Bacuez explains in The Divine Office: Considered From a Devotional Point of View p. 398,

Lauds, designed to be recited immediately after midnight, expresses the sentiments of a soul that entered the world in the sight of God and of His Perfections. It should express therefore the mind of Our Lord at His Nativity, or at the opening of His glorious Life at the Resurrection. This is what we accordingly meet with especially in the Lauds of Sundays and festivals with which we are exclusively engaged: every part of them we find will suggest this thought.

Ibid. p. 412:

Canticle, Benedictus Dominus Deus.

The antiphons, little chapter and hymn vary according to the Office, and take their character from it; but the same Canticle with which Lauds ends is also its crown. Taken from the Holy Gospel this new Canticle that David seems to announce in the preceding psalm (cxlix. i) transports us all at once from the Old Law to the New, from promises and figures to the Incarnation and the Real Presence of the Son of God on earth. One of the last priests of the Order of Aaron, the first who had had any knowledge of the coming of our Saviour, celebrating in lofty language the graces that the Redeemer brings with Him to the earth, exalts, with a holy enthusiasm the vocation of his own son who was raised up to be the precursor of the Son of the Most High. What can be more fitted to touch the heart of a priest called, like S. John the Baptist, to announce the Word made flesh, to teach men the knowledge of salvation, and to conduct sinners to redemption by the path of penance?