The Lion hath roared: who will not fear? The Lord God hath spoken: who can but prophesy? - that is, there is cause for you to fear, when the Lord "roareth from Zion;" but if ye fear not, God's prophets dare not but fear. So Paul saith, "necessity is laid upon me; yea, woe is unto me if I preach not the Gospel! For if I do this thing willingly, I have a reward; but if against my will, a dispensation" of the Gospel "is committed unto me" 1-Corinthians 9:16-17; and Peter and John, "whether it be right in the sight of God to hearken unto you more than unto God, judge ye! For we cannot but speak the things which we have seen and heard" Acts 4:19-20; Moses was not excused, though slow of speech; nor Isaiah, though of polluted lips; nor Jeremiah, because he was a child; but God said, "Say not, I am child, for thou shalt go to all that I shall send thee, and whatsoever I command thee, thou shalt speak" Jeremiah 1:7. And Ezekiel was bidden, "be not rebellious, like that rebellious house" Ezekiel 2:8. And when Jeremiah would keep silence, he saith, "His Word was in mine heart as a burning fire, shut up in my bones, and I was weary with forbearing and I could not stay" Jeremiah 20:9.

The lion hath roared - God hath sent forth a terrible alarm, Who will not fear? Can any hear such denunciations of Divine wrath and not tremble?
The Lord God hath spoken - And those only who are in communion with him have heard the speech. Who can but prophesy? Who can help proclaiming at large the judgment threatened against the nation?
But I think נבא naba, here, is to be taken in its natural and ideal signification, to pray, supplicate, or deprecate vengeance. The Lord hath spoken of punishment - who can help supplicating his mercy, that his judgments may be averted?

The lion hath roared, who will not fear? the Lord GOD hath spoken, who can but (i) prophesy?
(i) Because the people always murmured against the Prophets, he shows that God's Spirit moved them to speak as they did.

The lion hath roared, who will not fear?.... Amos said this from his own experience, who, having been a herdsman in the wilderness of Tekoa, had often heard a lion roar, which had put him into a panic, both for himself, and the cattle he kept; the figure is explained in the next clause:
the Lord God hath spoken, who can but prophesy? whether it be to foretell future events, which the Lord has made known shall come to pass; or to preach the word, which is to prophesy to edification, to exhortation, and comfort, 1-Corinthians 14:3; or to perform the more private exercises of religion, as singing of psalms, praying, &c. 1-Chronicles 25:1; these things who can forbear doing, to whom the Lord has spoken either in a dream or vision, or in his word, and by his Spirit; and to whom he has given a call and commissions, and gifts and graces, qualifying them for such service? who that has the fear of God in his heart, and his glory in view, and the good of others, that can refrain from it? nay, it is of dangerous consequence to refuse it; for if the roaring of a lion is so terrible, and if the wrath of an earthly king is as the roaring of a lion, much more the wrath and displeasure of the King of kings. Jonah declined prophesying when the Lord spoke to him, but what was the consequence of it? the prophet by this seems to justify himself in prophesying, and that he ought not to be blamed for it, seeing the Lord had given him the word, and therefore he ought to publish it. This may be particularly applied to the ministers of the word, who have a call, a charge and gifts from Christ, and on whom there is a necessity laid to preach the Gospel; and who should not shut, to declare it on any account; nor can they, who have it in their hearts, and as fire in their bones; who have seen and heard, and handled of the word of life, let what will be the consequence of it; see Psalm 68:11.

As when "the lion roars" (compare Amos 1:2; Amos 3:4), none can help but "fear," so when Jehovah communicates His awful message, the prophet cannot but prophesy. Find not fault with me for prophesying; I must obey God. In a wider sense true of all believers (Acts 4:20; Acts 5:29).

Hath roared - As a lion roareth when near his prey: so God hath terribly threatened what is near to be done. Prophesy - Amos can not but speak what he had heard.