Will a lion roar in the forest, when he hath no prey? will a young lion cry out of his den, if he have taken nothing?
Will a lion roar in the forest when he hath no prey? The same idea as in Matthew 24:28. Where a corrupt nation is, there God's instruments of punishment are sure also to be. The lion roars loudly only when he has prey in sight.
Will a young lion cry out of his den if he (the "lion," not the "young lion").
Have taken nothing? The young lion just weaned lies silent until the old lion brings the prey near; then the scent rouses him. So the prophet would not speak against Israel if God did not reveal to him Israel's sins as requiring punishment. The effect must follow the cause. God's command to denounce judgment upon the guilty is the cause: Amos' prophesying is the effect.