The liturgy is peppered with short prayers and exchanges.  One of the standard dialogues found throughout the Prayer Book begins “The Lord be with you“.  Among his analysis of the Prayer Book in 17th century, the Rev. Dr. John Boys pointed out that

The novelists have censured this, and other like suffrages, as short cuts, or shreddings, rather than wishings, or prayers.

The “novelists” are his word for the Puritans of his day, who sought a new (hence, novel) form of liturgy that relied more upon long extemporaneous prayers said by the minister, rather than the series of short and succinct prayers of the historic liturgy such as in the Prayer Book.  Citing a few scriptural and Early Church examples of short-but-pious prayers, Boys describes them as

as if they were darts thrown out with a kind of sudden quickness, lest that vigilant and erect attention of mind, which in devotion is very requisite, should be wasted and dulled through continuance, if their prayers few, and long.  The same father in the same place [St. Augustine, Epistle 121], “For oftentimes more is accomplished by groans than by speeches, more by weeping, than by blowing.”  Peruse that learned epistle, for it is a sufficient apology, both for the length of our whole service, and also for the shortness of our several prayers.  If Augustine now lived, and were made umpire between the novelists and us, he would rather approve many short prayers in England, than those two long prayers, one before and the other after sermon, in Scotland and Geneva.

“An Exposition of the Several Offices adapted for various occasions of Public Worship…”
by the Rev. Dr. John Boys, 1629; printed by the Rev. Kensey Stewart, 1851 (page 41)

The impatient 21st-century American may look at the Prayer Book and think our Prayers of the People and Prayer of Consecration to be quite long, but just look at some Puritan and other ‘Reformed’ liturgies, such as in this book, and you will discover just what “long” really means!  This is not to say that long prayers are inherently bad, but they are overly demanding upon the attentions, affections, and memory of the hearer.

As for the phrase “the Lord be with you“, Boys comments that it is primarily derived from Ruth 2:4 “as a usual salutation among God’s people“, citing also Judges 6:12 and Luke 1:28.  He considers other salutations like “God speed,” and “God save you”, and “God bless you” as being equivalent in holiness and worthy of Christian discourse.