When the Lord shall build up Zion - The Septuagint, the Latin Vulgate, and Luther, vender this, "Because the Lord hath built up Zion." This also is the most natural and correct translation of the Hebrew. The reference, however, may be to the future. The psalmist may throw himself into the future, and - standing there - he may describe things as they will appear then - as already done.
He shall appear in his glory - The idea is that the building up of Zion would be an occasion in which God would manifest his glory. In reference to the restoration of his people from bondage; in rebuilding Zion, then in ruins; in restoring the splendor of the place where he had been so long worshipped, he would display his true character as a God of glory, truth, power, and goodness. As applied to the church in general, this would mean that when God comes to revive religion, to visit his people, to recover them from their backslidings, to convert and save sinners, he appears in his appropriate character as the God of his people - as a glorious God. Then the perfections of his nature are most illustriously displayed; then he appears in his true character, as a God of mercy, grace, and salvation. There is no scene on earth where the character of God is more gloriously exhibited than in a revival of true religion.

When the Lord shall build up Zion - It is such a difficult thing, so wholly improbable, so far out of the reach of human power, that when God does it, he must manifest his power and glory in a most extraordinary manner.

When the LORD shall build up Zion, he shall appear (m) in his glory.
(m) That is, when he will have drawn his church out of the darkness of death.

When the Lord shall build up Zion,.... The church of God, fallen down, and in a ruinous condition, as it may be said to be when the doctrines of the Gospel are departed from; the ordinances of it are corrupted and altered, or not attended to; the worship and discipline of the Lord's house are neglected; great declensions in faith, love, and zeal, among the professors of religion, and but few instances of conversion: and it may be said to be built up again, as it will be in the latter day, when the doctrines of grace will be revived; the ordinances will be administered in their primitive purity; great spirituality, holiness, and brotherly love, among the saints, and large numbers converted and brought into it: and this will be the work of Christ, the great master builder; the materials of this building are the saints, those lively stones which will now be laid with fair colours; the ministers of the word will be the instruments that Christ will make use of in rebuilding his church; it is his Spirit, power, and grace, which will make all effectual; and he will have the glory, as follows: the Targum is,
"for the city of Zion is built by the Word of the Lord:''
he shall appear in his glory; or "shall be seen in his glory" (b), which will be upon his church and people, and on which there will be a defence, so that it shall continue; and this will lie chiefly in the purity of Gospel truths, ordinances, and worship; in the number of converts; in the gifts and graces of the Spirit of God upon them; in their peace, prosperity, unity, and spirituality; and in the presence of Christ with them, who will be seen in all the glory and majesty of his kingly office; he will now reign before his ancients gloriously.
(b) "videbitur", V. L. Pagninus, Montanus.

When the Lord shall build--or better, "Because the Lord hath built," &c., as a reason for the effect on others; for in thus acting and hearing the humble, He is most glorious.