[On the Beatitudes: Matthew 5:1-9].
When our Lord Jesus Christ, beloved, was preaching the gospel of the Kingdom, and was healing divers sicknesses through the whole of Galilee, the fame of His mighty works had spread into all Syria.
Large crowds too from all parts of Judæa were flocking to the heavenly Physician (cf. Matt. 4:23-24).
For as human ignorance is slow in believing what it does not see, and in hoping for what it does not know, those who were to be instructed in the divine lore, needed to be aroused by bodily benefits and visible miracles.
This was so that they might have no doubt as to the wholesomeness of His teaching when they actually experienced His benignant power.
And therefore, that the Lord might use outward healings as an introduction to inward remedies, and after healing bodies might work cures in the soul, He separated Himself from the surrounding crowd, ascended into the retirement of a neighbouring mountain, and called His apostles to Him there.
This He did in order that from the height of that mystic seat He might instruct them in the loftier doctrines, signifying from the very nature of the place and act that He it was who had once honoured Moses by speaking to him: then indeed with a more terrifying justice, but now with a holier mercifulness, that what had been promised might be fulfilled when the Prophet Jeremiah says:
“behold the days come when I will complete a new covenant for the house of Israel and for the house of Judah. After those days, saith the Lord, I will put My laws in their minds, and in their heart will I write them” (Jer. 31:31-33; cf. Heb. 8:8–12).
He therefore who had spoken to Moses, spoke also to the apostles, and the swift hand of the Word wrote and deposited the secrets of the new covenant in the disciples’ hearts.
There were no thick clouds surrounding Him as of old, nor were the people frightened off from approaching the mountain by frightful sounds and lightning (cf. Heb. 12:18ff), but quietly and freely His discourse reached the ears of those who stood by, so that the harshness of the law might give way before the gentleness of grace, and “the spirit of adoption” might dispel the terrors of bondage (cf. Rom. 8:15).
The nature then of Christ’s teaching is attested by His own holy statements: that they who wish to arrive at eternal blessedness may understand the steps of ascent to that high happiness. “Blessed,” He saith, “are the poor in spirit, for theirs is the kingdom of heaven” (Matt. 5:3).
Leo the Great (c.400-461): Sermon 95, 1-2.