And suddenly there was present with the angel a multitude of the heavenly host, praising God, and saying, Glory in the highest to God, and on earth peace, among men good-will. Luke 2:13-14
“And suddenly there was present with the angel a multitude. An exhibition of divine splendor had been already made in the person of a single angel. But God determined to adorn his own Son in a still more illustrious manner, This was done to confirm our faith as truly as that of the shepherds. Among men, the testimony of “two or three witnesses” (Matthew 18:16) is sufficient to remove all doubt. But here is a heavenly host, with one consent and one voice bearing testimony to the Son of God. What then would be our obstinacy, if we refused to join with the choir of angels, in singing the praises of our salvation, which is in Christ? Hence we infer, how abominable in the sight of God must unbelief be, which disturbs this delightful harmony between heaven and earth. Again, we are convicted of more than brutal stupidity, if our faith and our zeal to praise God are not inflamed by the song which the angels, with the view of supplying us with the matter of our praise, sang in full harmony. Still farther, by this example of heavenly melody, the Lord intended to recommend to us the unity of faith, and to exhort us to join with one consent in singing his praises on earth.
Glory to God in the highest. The angels begin with thanksgiving, or with the praises of God; for Scripture, too, everywhere reminds us, that we were redeemed from death for this purpose, that we might testify with the tongue, as well as by the actions of the life, our gratitude to God. Let us remember, then, the final cause, why God reconciled us to himself through his Only Begotten Son. It was that he might glorify his name, by revealing the riches of his grace, and of his boundless mercy. And even now to whatever extent any one is excited by his knowledge of grace to celebrate the glory of God, such is the extent of proficiency in the faith of Christ. Whenever our salvation is mentioned, we should understand that a signal has been given to excite us to thanksgiving and to the praises of God.” John Calvin, Commentary on Luke 2