For the Lord is a God of justice;
    blessed are all those who wait for him.  (Isaiah 30:18b)

The Hebrew word translated ‘justice’ is מִשְׁפָט mishpat, and covers a range of meaning, that includes all things related to judgment, regulation and condemnation.  It upholds that justice is served when transgression is punished.  

Made in God’s image, humankind seeks perfect justice and finds the world lacking it.  Scripture affirms this, asserting that, seen through a temporal lens, justice can only be found at two events, the cross and the final judgment.  Thus, it is important to wait for justice to be done.

This is expressed in another way by Paul, here speaking to fellow disciples and those within the body of Christ regarding the final judgment:

Beloved, never avenge yourselves, but leave it to the wrath of God, for it is written, “Vengeance is mine, I will repay, says the Lord.”  (Romans 12:19)

Paul states this for two reasons; first, that the authentic follower of Christ gives up his or her quest for earthly justice that so consumes the world. Railing against the patent injustice they see about them, a Christian might be tempted to fix God’s creation, which at best futile and misguided, but at worse, a distraction from the commission to bring and teach the truth of the Gospel. 

The second reason is that the journey of repentance is one of forgiveness, remembering that to forgive literally means to ‘away-give’ or give away all thought of settling scores, righting personal wrongs and seeking reparation.

But as we read in the quotation from Romans, citing Deuteronomy (32:25), wrath proceeds judgment.  That ‘the Lord is a God of justice’ can only be so because he wholly good, prefect and true – in other words, holy.  There is no manner or form in which God can accept anything that opposes his purpose or attempts to impugn his nature.  Wrath is His settled repudiation and is ‘poured out’ on humanity.

… it is God who executes judgement,
    putting down one and lifting up another.
For in the hand of the Lord there is a cup
    with foaming wine, well mixed,
and he pours out from it,
    and all the wicked of the earth
    shall drain it down to the dregs.  (Psalm 75:7-8) 

Of course, the first manifestation of this is the cross, where God’s wrath is inflicted on his Son, Jesus, who in obedience to his Father, drinks the bitter cup on behalf of those who believe in him and are justified (gain God’s judicial approval). From Matthew, we read of his agony in Gethsamene, on the eve of his crucifixion:

(Jesus) fell on his face and prayed, saying, ‘My Father, if it be possible, let this cup pass from me; nevertheless, not as I will, but as you will…’ (Matthew 26:39)

And again:

‘My Father, if this cannot pass unless I drink it, your will be done.’  (Ibid 26:42)

While for those who do not believe and therefore do not receive God’s judicial approval, terrible wrath and judgment fall on their heads.

The book of Revelation describes how this looks on earth, the apostle John is witness:

‘Then I heard a loud voice from the temple telling the seven angels, ‘go and pour out on the earth the seven bowls of the wrath of God.’  (Revelation 16:1)

 Here is an example, that of the fourth bowl:

The fourth angel poured out his bowl on the sun, and it was allowed to scorch people with fire. They were scorched by the fierce heat, and they cursed the name of God who had power over these plagues. They did not repent and give him glory.  (Ibid 16:8-9)

And God is entitled, John overhears this from another angel:

‘Just are you, O Holy One, who is and who was,
    for you brought these judgements.

For they have shed the blood of saints and prophets,
    and you have given them blood to drink.
It is what they deserve!’  (Ibid 16:5-6)

Of course, viewed eternally the judgment of the cross and that of the final judgment cannot be separated.  Indeed, John record in his gospel and his vision, one phrase that demonstrates the singularity, although rendered differently in the Greek using the verbs, τελέω teleó and γίνομαι ginomai, respectfully,

From the cross, Jesus does drink the bitter cup in the temporal:

When Jesus had received the sour wine, he said, it is finished’, and he bowed his head and gave up his spirit.  (John 19:30)

While in the eternal:

The seventh angel poured out his bowl into the air, and a loud voice came out of the temple, from the throne, saying, ‘it is done!’ (Revelation 16:17)  

God’s perfect justice is seen in punishing either his Son or people who reject him.  There is no escaping that there must be propitiation for a just God.  This is central truth of the Gospel, unpalatable to many, but inescapable to all.  For all shall worship, willingly or unwillingly.

… at the name of Jesus every knee should bow, in heaven and on earth and under the earth, and every tongue confess that Jesus Christ is Lord, to the glory of God the Father.  (Philippians 2:10-11)

It is at this event, the cross and judgment that mercy, grace and justice combine to those who would have faith:

God shows his love for us in that while we were still sinners, Christ died for us.  Since, therefore, we have now been justified by his blood, much more shall we be saved by him from the wrath of God.  (Romans 5:8-9)

Paul expresses this another way:

 But God, being rich in mercy, because of the great love with which he loved us, even when we were dead in our trespasses, made us alive together with Christ -by grace you have been saved -and raised us up with him and seated us with him in the heavenly places in Christ Jesus, so that in the coming ages he might show the immeasurable riches of his grace in kindness towards us in Christ Jesus.  (Ephesians 2:4-7)