In that day this song will be sung in the land of Judah: “We have a strong city; he sets up salvation as walls and bulwarks. Open the gates, that the righteous nation that keeps faith may enter in. You keep him in perfect peace whose mind is stayed on you, because he trusts in you. Trust in the LORD forever, for the LORD GOD is an everlasting rock. For he has humbled the inhabitants of the height, the lofty city. He lays it low, lays it low to the ground, casts it to the dust. The foot tramples it, the feet of the poor, the steps of the needy.”
Not everyone who says to me, ‘Lord, Lord,’ will enter the kingdom of heaven, but the one who does the will of my Father who is in heaven.
Everyone then who hears these words of mine and does them will be like a wise man who built his house on the rock. And the rain fell, and the floods came, and the winds blew and beat on that house, but it did not fall, because it had been founded on the rock. And everyone who hears these words of mine and does not do them will be like a foolish man who built his house on the sand. And the rain fell, and the floods came, and the winds blew and beat against that house, and it fell, and great was the fall of it.
The hope of Advent is the hope of righteousness. Only “the righteous nation” enters the kingdom. Only the one who “does the will” of the Father and “does” the words of the Son will enter the kingdom.
As an aside, we see again the subtle yet unmistakable way in which Scripture demonstrates the equality of the Father and the Son. God leaves things obscure enough for heretics to condemn themselves, but plain enough for believers to have faith. Who will enter the kingdom? The one who obeys the Father? Who will have a house of strong walls (cf. Is. 26:1)? The one who obeys the Son. So we are left with only few options. Either that Father and Son share in power and glory and essence so that their will is one; or there are at least two ways to enter the kingdom. And if there are two, why can there not be three, or four, or five, ad infinitum? All the Father has in his essence the Son has, saving Fatherhood.
But what is the way to enter the kingdom? A cursory reading of these texts points plainly to works. Good people will enter the kingdom and bad people will not. That is all well and good, if the Bible did not also teach that there are none good. A careful reading of these passages demonstrates the true requirement of entering the kingdom.
In Isaiah the righteous nation enters in. But what is the nature of this righteousness? The righteous nation is the nation that “keeps faith,” or, remain faithful. They are further described as “poor” and “needy.” In other words, they have nothing of worth in themselves to claim. They are the “poor in spirit.” Everything they receive from God is graced to them; none of it is earned. They can offer nothing.
In Matthew, they do the will of the Father and the Son. Yet the verses 22 and 23 clearly address the issue of “which came first: righteousness or salvation.” Matthew 7:22 leaves no doubt that man is not saved by doing righteous deeds. On the last day people will stand before Jesus with a laundry list of their good deeds and be promptly dismissed to eternal destruction. In the next verse Jesus makes plain the entrance requirements of the kingdom: personal knowledge. If Jesus does not know you, you are not getting into his kingdom.
Only the righteous will enter the kingdom of heaven. But the righteousness of the righteous is not their own. They are faithful because they have believed and cried out to God for aid. They do the will of the Father and Son because Jesus has identified himself with them. All of their righteousness is found from God. All of the righteousness is found in Christ.