John Calvin Commentary Isaiah 27:1

"In that day Jehovah with his hard and great and strong sword will punish leviathan the swift serpent, and leviathan the crooked serpent; and he will slay the monster that is in the sea." — Isaiah 27:1 (ASV)

In that day. Here the Prophet speaks generally of the judgment of God, and thus includes the whole of Satan’s kingdom. Having previously spoken of the vengeance of God to be displayed against tyrants and wicked men who have shed innocent blood, he now proceeds further and publishes the proclamation of this vengeance.

On leviathan. The word “leviathan” is variously interpreted, but generally, it simply denotes either a large serpent, or whales and sea-fishes, which approach the character of monsters on account of their huge size. Although this description applies to the king of Egypt, yet under one class, he also intended to include the other enemies of the Church.

For my own part, I have no doubt that he speaks allegorically of Satan and of his whole kingdom, describing him under the figure of some monstrous animal, and at the same time alluding to the crafty wiles by which he glosses over his mischievous designs. In this manner, he intended to address many doubts by which we are continually assailed when God declares that he will assist us, and when we experience, on the other hand, the strength, craft, and deceitfulness of Satan. Wonderful are the stratagems with which he comes prepared for doing mischief, and dreadful the cruelty which he exercises against the children of God.

But the Prophet shows that all this will not prevent the Lord from destroying and overthrowing this kingdom. It is indeed certain that this passage does not relate to Satan himself, but to his agents or instruments, by which he governs his kingdom and annoys the Church of God. Now, though this kingdom is defended by innumerable cunning devices and is astonishingly powerful, yet the Lord will destroy it.

To convince us of this, the Prophet contrasts with it the Lord’s sword, hard, and great, and strong, by which he will easily slay an enemy that is both strong and crafty. We should therefore observe that we continually have to do with Satan as with some wild beast, and that the world is the sea in which we sail. We are beset by various wild beasts, which endeavor to upset our ship and sink us to the bottom, and we have no means of defending ourselves and resisting them if the Lord does not aid us.

Accordingly, by this description, the Prophet intended to describe the greatness of the danger that threatens us from enemies so powerful and so full of rage and of cunning devices. We would quickly be reduced to the lowest extremity and would be utterly ruined if God did not oppose and meet them with his invincible power, for by his sword alone can this pernicious kingdom of Satan be destroyed.

But we must observe what he says in the beginning of the verse, In that day. It means that Satan is permitted, for some time, to strengthen and defend his kingdom, but that it will eventually be destroyed, as Paul also declares, “God will quickly bruise Satan under your feet” (Romans 16:20). By this promise, he shows that the time for war is not yet ended, and that we must fight bravely until that enemy is subdued, who, though he has been vanquished a hundred times, does not cease to renew the warfare. We must therefore fight with him continually and must resist the violent attacks which he makes upon us; but, so that we may not be discouraged, we must keep our eye on that day when his strong arm will be broken.

On leviathan the piercing serpent, and on leviathan the crooked serpent. The epithets applied to “leviathan” describe, on the one hand, his tricks and wiles, and, on the other hand, his open violence, but at the same time intimate that he is endowed with invincible power. Since בריח (bārīăch) signifies a crowbar, that word metaphorically denotes the power of piercing, either on account of venomous bites or on account of open violence. The second name, עקלתון (gnăkāllāthōn), is derived from the verb עקל (gnākăl), to bend; and so it comes to be applied to crooked and tortuous foldings.