He swalloweth the ground - He seems as if he would absorb the earth. That is, he strikes his feet into it with such fierceness, and raises up the dust in his prancing, as if he would devour it. This figure is unusual with us, but it is common in the Arabic. See Schultens, "in loc.," and Bochart, "Hieroz," P. i. L. ii. c. viii. pp. 143-145. So Statius:
Stare loco nescit, pereunt vestigia mille
Ante fugam, absentemque ferit gravis ungula campum.
Th' impatient courser pants in every' vein,
And pawing seems to beat the distant plain;
Hills, vales, and floods, appear already cross'd,
And ere he starts a thousand steps are lost.
Pope
Neither believeth he that it is the sound of the trumpet - This translation by no means conveys the meaning of the original. The true sense is probably expressed by Umbreit. "He standeth not still when the trumpet soundeth; "that is, he becomes impatient; he no longer confides in the voice of the rider and remains submissive, but he becomes excited by the martial clangor, and rushes into the midst of the battle. The Hebrew word which is employed (יאמין ya'âmiyn) means properly "to prop, stay, support"; then "to believe, to be firm, stable"; and is that which is commonly used to denote an act of "faith," or as meaning "believing." But the original sense of the word is here to be retained, and then it refers to the fact that the impatient horse no longer stands still when the trumpet begins to sound for battle.

He (o) swalloweth the ground with fierceness and rage: neither believeth he that [it is] the sound of the trumpet.
(o) He so rides the ground that it seems nothing under him.

He swalloweth the ground with fierceness and rage,.... Being so eager for the battle, and so full of fierceness and rage, he bounds the plain with such swiftness that he seems rather to swallow up the ground than to run upon it;
neither believeth he that it is the sound of the trumpet; for joy at hearing it; or he will not trust to his ears, but will see with his eyes whether the battle is ready, and therefore pushes forward. Mr. Broughton and others read it, "he will not stand still at the noise of the trumpet"; and the word signifies firm and stable, as well as to believe; when he hears the trumpet sound, the alarm of war, as a preparation for the battle, he knows not how to (a) stand; there is scarce any holding him in, but he rushes into the battle at once, Jeremiah 8:6.
(a) "Stare loco nescit". Virgil. Georgic. l. 3. v. 84. "Ut fremit acer equus", &c. Ovid. Metamorph. l. 3. Fab. 10. v. 704.

swalloweth--Fretting with impatience, he draws the ground towards him with his hoof, as if he would swallow it. The parallelism shows this to be the sense; not as MAURER, "scours over it."
neither believeth--for joy. Rather, "he will not stand still, when the note of the trumpet (soundeth)."

Swalloweth - He is so full of rage and fury, that he not only champs his bridle, but is ready to tear and devour the very ground on which he goes. Believeth - He is so pleased with the approach of the battle, and the sound of the trumpet calling to it, that he can scarce believe his ears for gladness.