2 “O sing unto the Lord a new song; sing unto the Lord, all the earth”. If all the earth sings a new song, it is thus building while it sings: the very act of singing is building: but only, if it sings not the old song. The lust of the flesh sings the old song: the love of God sings the new....Hear why it is a new song: the Lord says, “A new commandment I give unto you, that you love one another.” The whole earth then sings a new song: there the house of God is built.
All the earth is the house of God. If all the earth is the house of God, he who clings not to all the earth, is a ruin, not a house; that old ruin whose shadow that ancient temple represented. For there what was old was destroyed, that what was new might be built up....The Apostle binds us together into this very structure, and fastens us when bound together in that unity, saying, “Forbearing one another in love; endeavouring to keep the unity of the Spirit in the bond of peace.” Where there is this unity of Spirit, there is one stone; but one stone formed out of many.
How one formed out of many? By forbearing one another in love. Therefore the house of the Lord our God is in building; it is this that is being wrought, for this are these words, for this these readings, for this the preaching of the Gospel over the whole world; as yet it is in building. This house has increased greatly, and filled many nations: nevertheless, it has not yet prevailed through all nations: by its increase it has held many, and will prevail over all: and it is gainsaid by those who boast of their being of its household, and who say, it has already lost ground.
It still increases, still all those nations which have not yet believed are destined to believe; that no man may say, will that tongue believe? will the barbarians believe? What is the meaning of the Holy Spirit having appeared in the fiery tongues, except that there is no tongue so hard that it cannot be softened by that fire? For we know that many barbarous nations have already believed in Christ: Christ already possesses regions where the Roman empire has never yet reached; what is as yet closed to those who fight with the sword, is not closed to Him who fights with wood.
For “the Lord has reigned from the wood.” Who is it who fights with wood? Christ. With His cross He has vanquished kings, and fixed upon their forehead, when vanquished, that very cross; and they glory in it, for in it is their salvation. This is the work which is being wrought, thus the house increases, thus it is building: and that you may know, hear the following verses of the Psalm: see them labouring upon, and constructing the house. “O sing unto the Lord all the earth.”
Source: The Enarrations, or Expositions, on the Psalms (New Advent)