Isaiah 58:1

For also when God saw the dying condition of the Jews who of their own will stopped their ears, and blinded their eyes, and made thick their hearts against the remembrance of the knowledge of God, He stirred up Isaiah to rouse them up, and cried to him to cry into their ears, saying, "Cry with thy throat, and spare not, and lift up thy voice like a trumpet, and shew My people their iniquity, and the house of Jacob their sins".

We are commanded then to cry out and to cry forcefully and not to spare our voice, lest we lose our salvation. "And do not be sparing," he says. That is, do not pass over the sinner's wickedness by keeping silent and by being considerate of his shame but inconsiderate of his well-being, for by keeping silent you have made worse the wounds that you ought to have healed by crying out.… We know that a trumpet is usually not so much heard as dreaded; it is not so much accustomed to bring pleasure as to inspire fear. A trumpet is necessary for sinners; it not only penetrates their ears but should strike their heart as well; it should not delight with its melody but chastise when it has been heard; it should encourage the bravehearted to righteousness, while it should turn the cowardly from their crimes.

(Chapter 58—Verse 1.) Cry aloud, spare not, lift up thy voice like a trumpet, and declare unto my people their transgression, and to the house of Jacob their sins. (LXX: Cry aloud, spare not, lift up thy voice like a trumpet, and declare unto the people their transgression, and to the house of Jacob their sins.) After finishing the previous chapter, in which peace is proclaimed to the righteous and no rest is given to the wicked, God commands the prophet Isaiah to cry aloud in strength, and to exalt his voice like a trumpet, and not to fear to declare the sins and transgressions of the people of Israel, neither fearing death nor the insults and threats of the wicked, but rather considering the Lord who rules over all. And because they have deaf ears and can barely hear, according to Symmachus and Aquila, they should turn their throat into a trumpet, which is called a shofar in Hebrew, and which they have interpreted as 'horn made of horn'. And indeed, when it was said to the Apostles, 'Ascend to the high mountain, you who evangelize Zion: lift up your voice with strength, you who evangelize Jerusalem: lift it up, do not be afraid' (Isaiah 40:9), neither a trumpet nor a horn is mentioned, but they are commanded to ascend the mountain. But because they were sinners whom he had to announce, and they dwelt below, the prophet is not commanded to ascend the mountain, but only to raise his voice like a trumpet and announce to them the coming wars. Otherwise, on the day of judgment, when it is said that the dead will rise in the resurrection and at the last trumpet, it is written, for the trumpet will sound, and the dead will rise incorruptible, so that just as they will be judged at the sound of the trumpet, so may Israel, dead in sin, hear its own crimes; at the same time, it is referred to as the people of God, so that they may learn what kind of father they have lost, who even calls his people sinners.