The city's walls are salvation. There is no need to name the architect of these fortifications. One hand only can pile their strength. God appoints salvation in lieu of all visible defences. Whom He purposes to save are saved. Whom He wills to keep safe are kept safe. They who can shelter behind that strong defence need no other. Weak, sense-governed hearts may crave something more palpable, but they do not really need it. A parapet on an Alpine road gives no real security, but only satisfies imagination. The sky needs no pillars to hold it up.
Then an unknown voice breaks in upon the song, calling on unnamed attendants to fling wide the gates. The city is conceived of as empty; its destined inhabitants must have certain qualifications. They must be righteous, and must 'keep faithfulness' being true to the God who is 'faithful and true' in all His relations. None but the righteous can dwell in conscious citizenship with the Unseen while here, and none but the righteous can enter through the gates into the city. That requirement is founded in the very nature of the case, and is as emphatically proclaimed by the gospel as by the prophet. But the gospel tells more articulately than he was enlightened to do, how righteousness is to be won. The last vision of the Apocalypse, which is so like this song in its central idea, tells us of the fall of Babylon, of the descent to earth of the New Jerusalem, and leaves as its last message the great saying, 'Blessed are they that wash their robes that they may ... enter in through the gate into the city.'
Our song gives some hint of similar thoughts by passing from the description of the qualifications for entrance to the celebration of the security which comes from trust. The safety which is realised within the walls of the strong city is akin to the 'perfect peace' in which he who trusts is kept; and the juxtaposition of the two representations is equivalent to the teaching that trust, which is precisely the same as the New Testament faith, is the condition of entrance. We know that faith makes righteous, because it opens the heart to receive God's gift of righteousness; but that effect of faith is implied rather than stated here, where security and peace are the main ideas. As some fugitives from the storm of war sit in security behind the battlements of a fortress, and scarcely hear the din of conflict in the open field below, the heart, which has taken refuge by trust in God, is kept in peace so deep that it passes description, and the singer is fain to give a notion of its completeness by calling it 'peace, peace.' The mind which trusts is steadied thereby, as light things lashed to a firm stay are kept steadfast, however the ship toss. The only way to get and keep fixedness of temper and spirit amid change and earthquake is to hold on to God, and then we may be stable with stability derived from the foundations of His throne to which we cling.
Therefore the song breaks into triumphant fervour of summons to all who hear it, to 'trust in Jab Jehovah for ever,' Such settled, perpetual trust is the only attitude corresponding to His mighty name, and to the realities found in His character. He is the 'Bock of Ages' the grand figure which Moses learned beneath the cliffs of Sinai and wove into his last song, and which tells us of the unchanging strength that makes a sure hiding-place for all generations, and the ample space which will hold all the souls of men, and be for a shadow from the heat, a covert from the tempest, a shelter from the foe, and a home for the homeless, with many a springing fountain in its clefts.