They set their mouths against heaven, and their tongues strut across the earth. Psalm 73:9

Psalm 73:9
"They set their mouths against heaven, and their tongues strut across the earth."

Spurgeon:

Against God himself they aim their blasphemies. One would think, to hear them, that they were demi-gods themselves, and held their heads above the clouds,

"They set their mouths against heaven, and their tongues strut across the earth."

...for they speak down upon other men as from a sublime elevation peculiar to themselves. Yet they might let God alone, for their pride will make them enemies enough without their defying him.

"their tongues strut"

Leisurely and habitually they traverse the whole world to find victims for their slander and abuse. Their tongue prowls in every corner far and near, and spares none. They affect to be universal censors, and are in truth perpetual vagrants.

"They set their mouths against heaven, and their tongues strut across the earth."

Like the serpent, they go nowhere without leaving their slime behind them; if there were another Eden to be found, its innocence and beauty would not preserve it from their filthy trail.

"They set their mouths against heaven, and their tongues strut across the earth."

They themselves are, beyond measure, worthy of all honour, and all the rest of mankind, except a few of their parasites, are knaves, fools, hypocrites, or worse.

When these men's tongues are out for a walk, they are unhappy who meet them, for they push all travellers into the kennel: it is impossible altogether to avoid them, for in both hemispheres they take their perambulations, both on land and sea they make their voyages.

The city is not free from them, and the village swarms with them. They waylay men in the king's highway, but they are able to hunt across country, too. Their whip has a long lash, and reaches both high and low. (Spurgeon, Treasury of David, 1885)

Edward Parry:

"Their tongue walketh through the earth." This shows the boundless and unlimited disorder of the tongue.

"Their tongue walketh through the earth," and leaves nothing unspoken of. If men be poor, they talk of oppressing and mastering of them; if they oppose, they discourse of violence and suppressing

Their tongue walketh through the earth." If in this perambulation they meet with truth, they darken it with lies and home-made inventions; if with innocence, they brand it with false accusations and bitter aspersions; if with a strict government and good laws, then they cry, "Let us break their bands asunder, and cast away their cords from us;" if with religion, they term it heresy, or superstition; if with patience, they term it obstinacy and perverseness; if with the church, they think of nothing less than devouring it, and cry, "Let us take the houses of God in possession;" if with the thoughts of a resurrection, and of future hopes, "Let us eat and drink," cry they, "for tomorrow we shall die."

"Their tongue walketh through the earth." Thus no corner is left unsearched by their abusive tongue, which walks through the earth. They may walk over the earth, but they will "set their mouth against the heavens." (Edward Parry, 1860)

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For more study on Psalm 73:
Psalm 73: A Corrective to a Modern Misunderstanding, Elmer A. Martens