William Burkitt on Revelation 8:1

When he had opened, that is, when the Lamb, who opened the six foregoing seals, did open the seventh, there was silence in heaven about half an hour, by way of allusion to what was done in the temple at the time of offering incense. The end of which silence was to give St. John an opportunity to contemplate those high mysteries which he had revealed to him, and to prepare him for new visions, as silence is cried before the proclamation of great and weighty matters. When great things are to be uttered, great attention is expected, and great silence prepares for great attention.