What is the significance of the little book in Revelation?

In Revelation 10, the little book symbolizes the gospel message and God's secret counsels, which are revealed to His servants. Only after John consumes the book, which is both sweet and bitter, is he permitted to prophesy, signifying that understanding God's message fully entails both the sweetness of salvation and the bitterness of witness to the suffering of Christ and the loss of those who reject Him. This encapsulates the dual nature of the Christian message — a joy to those who believe and a sorrow to those who do not.