Albert Barnes Commentary Luke 3:15

"And as the people were in expectation, and all men reasoned in their hearts concerning John, whether haply he were the Christ;" — Luke 3:15 (ASV)

In expectation. Expecting the Messiah. The marginal note says suspense. That is, they were not certain whether John himself was the Messiah. They confidently expected his appearing, and their minds were in suspense, or they were in a state of doubt whether he had already come, and whether John was the Messiah.

Mused in their hearts of John. They thought of his character, his preaching, and his success, and anxiously inquired whether he was not doing the things that were expected of the Messiah.