But he shall judge the poor with justice, and shall reprove with equity the meek of the earth: and he shall strike the earth with the rod of his mouth, and with the breath of his lips he shall slay the wicked. And justice shall be the girdle of his loins: and faith the girdle of his reins. Isaiah 11:4-5
The second of the Advent Antiphons deals with the longing for God's coming justice.
There is so much suffering and injustice in the world and we long for God's anointed to come and set things right. But often what we want is justice for others and mercy for ourselves.
God is both merciful and just, which is a combination of attributes that is often difficult for us to reconcile. Until Jesus returns to bring us into his kingdom of perfect compassion and justice, we are called to live lives of compassion and mercy.
O Lord and Ruler the house of Israel, who appeared to Moses in the flame of the burning bush and gave him the law on Sinai: come, and redeem us with outstretched arms.