258. Then I saw a strong angel proclaiming with a loud voice. (5:2) This symbolizes Divine truth flowing in from the Lord deeply into the thought of angels and people, and investigation.

In the spiritual sense an angel proclaiming means the Lord, because an angel does not proclaim and instruct on his own, but from the Lord, even though he does so as though on his own. The angel is called a strong angel because he acts with power, and something proclaimed with power flows deeply into the thought. A loud voice symbolizes Divine truth from the Lord with power or force.

Investigation is symbolically meant as well, because the angel asks, "Who is worthy to open the book?" which follows next.