John Calvin Commentary 2 Corinthians 10:4

"(for the weapons of our warfare are not of the flesh, but mighty before God to the casting down of strongholds)," — 2 Corinthians 10:4 (ASV)

For the weapons of our warfare. The warfare corresponds with the kind of weapons. He glories in being equipped with spiritual weapons. The warfare, accordingly, is spiritual. Therefore, it follows conversely, that it is not according to the flesh. In comparing the ministry of the gospel to a warfare, he uses a most apt comparison.

The life of a Christian, it is true, is a perpetual warfare, for whoever devotes himself to God's service will never have a truce from Satan, but will be harassed with constant turmoil. However, it is fitting for ministers of the word and pastors to be standard-bearers, leading the way for others; and certainly, Satan harasses no one more, assaults no one more severely, or subjects anyone to more numerous or dreadful attacks.

Therefore, anyone who prepares himself for this office is mistaken if he is not also equipped with courage and bravery for the struggle; for his work involves nothing but fighting. For we must realize that the gospel is like a fire that ignites Satan's fury. Therefore, it is inevitable that Satan will arm himself for a conflict whenever he sees the gospel advancing.

But with what weapons is Satan to be repelled? He can only be repelled by spiritual weapons. Therefore, whoever is not armed with the power of the Holy Spirit, no matter how much he may boast of being a minister of Christ, will not prove himself to be one.

Furthermore, if you want a complete list of spiritual weapons, doctrine must be combined with zeal, a good conscience with the effectiveness of the Spirit, and with other necessary graces. Let the Pope now go and claim apostolic dignity for himself! What could be more ridiculous, if we are to judge according to the rule Paul lays down here!

Mighty through God. Either according to God, or from God. I believe there is an implied antithesis here, so that this strength is contrasted with the weakness that appears outwardly to the world, and so, paying no attention to human judgments, he would seek God's approval for his fortitude. At the same time, the antithesis also holds true in another sense—that the power of his weapons depends on God, not on the world.

In the demolishing of fortresses. He uses the term fortresses to mean schemes and every high thing that exalts itself against God, about which we will find him speaking later. However, he designates them this way appropriately and expressively, for his purpose is to declare boldly that nothing in the world is so strongly fortified that he cannot overthrow it.

I am well aware how worldly people boast in their empty displays, and how disdainfully and recklessly they despise me, as if there were nothing in me but what is insignificant and contemptible, while they, meanwhile, stand on a lofty perch. But their confidence is foolish, for the armor of the Lord with which I fight will prevail against all the strongholds on which they rely, believing themselves to be invincible.

Now, since the world is accustomed to fortify itself in two ways for waging war against Christ—on the one hand, by cunning, wicked schemes, subtlety, and other secret plots; and, on the other hand, by cruelty and oppression—he addresses both these methods. For by schemes he means whatever pertains to worldly wisdom.

The term high thing refers to any kind of glory and power in this world. Therefore, there is no reason why a servant of Christ should fear anything, however formidable, that may oppose his doctrine. Let him persevere in spite of it, and he will scatter every plot of whatever kind to the winds.

Indeed, the kingdom of Christ cannot be established except by overthrowing everything in the world that is exalted. For nothing is more opposed to God's spiritual wisdom than the wisdom of the flesh; nothing is more contrary to God's grace than human natural ability, and so it is with other things. Therefore, the only foundation of Christ’s kingdom is the humbling of humanity.

And expressions from the Prophets speak to this effect:

The moon shall be ashamed, and the sun shall be confounded,
when the Lord shall begin to reign in that day (Isaiah 24:23).

Again,

The loftiness of man shall be bowed down, and the high looks of mortals shall be abased, and the Lord alone shall be
exalted in that day (Isaiah 5:15 and Isaiah 2:17).

Because, so that God alone may shine forth, it is necessary for the world's glory to vanish.