John Calvin Commentary Romans 2:5

"but after thy hardness and impenitent heart treasurest up for thyself wrath in the day of wrath and revelation of the righteous judgment of God;" — Romans 2:5 (ASV)

But according to your hardness, etc. When we become hardened against the admonitions of the Lord, impenitence follows; and those who are not concerned about repentance openly provoke the Lord.

This is a remarkable passage. From this we may learn what I have already referred to: the ungodly not only accumulate for themselves daily a heavier weight of God’s judgments as long as they live here, but the gifts of God, which they continually enjoy, will also increase their condemnation.

For an account of them all will be required. It will then be found that it will be justly imputed to them as an extreme wickedness that they were made worse by God’s bounty, by which they surely ought to have been improved. Let us then take heed, lest by the unlawful use of blessings we store up for ourselves this cursed treasure.

For the day, etc.; literally, in the day; but it is used for εἰς ἡμέραν, for the day. The ungodly now gather the indignation of God against themselves, the stream of which will then be poured on their heads. They accumulate hidden destruction, which will then be drawn out from the treasures of God.

The day of the last judgment is called the day of wrath when a reference is made to the ungodly, but it will be a day of redemption for the faithful. And thus, all other visitations of God are always described as dreadful and full of terror to the ungodly, and on the contrary, as pleasant and joyful to the godly. Therefore, whenever the Scripture mentions the approach of the Lord, it tells the godly to exult with joy; but when it turns to the reprobate, it proclaims nothing but dread and terror.

“A day of wrath,” says Zephaniah, “shall be that day, a day of tribulation and distress, a day of calamity and wretchedness, a day of darkness and of thick darkness, a day of mist and of whirlwind” (Zephaniah 1:15).

You have a similar description in Joel 2:2 and following. And Amos exclaims:

“Woe To You Who Desire The Day Of The Lord! What Will It Be To You? The Day Of The Lord Will Be Darkness, And Not Light.” (Amos 5:18).

Furthermore, by adding the word revelation, Paul indicates what this day of wrath will be — that the Lord will then manifest his judgment. Though he gives daily some indications of it, he yet suspends and holds back, until that day, the clear and full manifestation of it. For the books will then be opened; the sheep will then be separated from the goats, and the wheat will be cleansed from the tares.