John Calvin Commentary Isaiah 12:6

"Cry aloud and shout, thou inhabitant of Zion; for great in the midst of thee is the Holy One of Israel." — Isaiah 12:6 (ASV)

Shout and sing. He again exhorts the godly to rejoice in the Lord, at the same time reminding them what is the nature of true joy, and on what it is founded. We have no other happiness than to have God dwelling in the midst of us. Without this, our life would be wretched and unhappy, even if we had an abundance of other blessings and every kind of riches. Now, if our heart is set on our treasure (Matthew 6:21), this happiness will draw all our affections to itself.

The Holy One of Israel. He calls him the Holy One in order to inform us what he intends to prove himself to be to us while he dwells with us. That is, his majesty may not only fill our minds with reverence toward him (for it would at the same time overwhelm us with terror), but he may also be pleased to make us the objects of his special care, though separated from the rest of the world. He calls him the Holy One from the effect produced; for, by gathering us to himself, (Ephesians 1:10), and saving us by his grace, he may be said to sanctify us as his own possession. Accordingly, if God is with us, the conviction of his presence will fill us with inconceivable joy. It therefore follows that when he is absent, we continue to be exposed to grief and sadness.

By the words, Shout and sing, he means that when God magnifies his power in the midst of us, he gives us occasion for no ordinary joy. Again, by directly addressing the inhabitants of Zion, he suggests that not all are capable of so great a blessing, and at the same time indirectly exhorts them to maintain unity of faith, so that by being united to the Church, we may partake of this blessed joy.