We are accustomed to contemplating the joy in heaven over sinners repenting on earth, with the angels rejoicing such occasions. But few realise or appreciate the fact that a significant part of the longest and last “hallelujah chorus”written in the Bible is devoted to praise God. It seems today, to talk God’s rejoicing in his judgments is a concept out of character with his mercy and grace. This reticence on our part, however, only demonstrates how inadequate our views are, on the hand, of the exceeding sinfulness of sin and, on the other hand, of God’s justice and holiness.
Why should there be joy in heaven over a judgment? Because, first, it reminds us that God’s judgment is just and perfect and the every existence of sin cannot call God’s justice into question. Many, today, with famines and wars around, when natural disaster approaches, many flee and run for shelter, if at all possible. But there are those who seem almost transfixed by the disaster coming. They simply stand, look and wait until it eventually overcomes them, and some call God’s existence into question or at least His power because these evils exist. Their superficial, unbelieving questions fail to take into account even present-day judgment upon nations for their idolatry, heathenism and apostasy. But the day of judgment will silence all such questions.
But second, there is joy over judgment, because against the dark backdrop of God’s avenging wrath against sin, His people will shine as the stars forever. God’s judgment will only cause his saving grace and mercy to shine more brilliantly both to His own glory and the everlasting joy and thankfulness of the redeemed.
Third, there is joy over judgment because God’s promises in His infallible Word will assuredly be fulfilled! With the deepening apostasy, we tend to grow querulous and impatient. But God says, “wait…stand still”and, as Israel saw God’s judgment on the Egyptians in the returning billows of the Red Sea, so we, too, will see every evil consumed by the billows of God’s holy and righteous retributive justice!

this article is an eye opening for us to know that our God is a JUST God.
God loves us thats why he is Just
even though he’s a Just God..but still he is good and merciful