'Everyone who was there joined in worship'. Everyone should join in worship. There should be no observers or mute persons present. Worship is the highest exercise the soul of man can enjoy and one that occupies the angelic spirits at all times.
When Hezekiah came to the throne of Judah everyone joined in worship because they saw how great was the Lord and felt His blessing in their hearts. They knew what they had missed when Ahaz shut them out of the temple.
It does not need to be a large company that gathers. True worship is in spirit and takes place in the heart. Whether quiet or noisy, in large gathering or small, near or far, it can only take place when you see the Lord. When He is lifted up, all else recedes.