John Gill Commentary Luke 20:5

"And they reasoned with themselves, saying, If we shall say, From heaven; he will say, Why did ye not believe him?" — Luke 20:5 (ASV)

And they reasoned with themselves
Or "they thought with themselves", as the Syriac version; or "within themselves", as the Vulgate Latin, though they did not express it; or "one with another", as the Arabic version; they took counsel together, and debated the matter among themselves, and reasoned after this manner:

saying, if we shall say from heaven ;
which was what, in their own consciences, they believed to be true,

he will say, why then believed ye him not ?
in what he said concerning the Messiah; which if they had, as they should, there would have been no reason for such a question they had put; (See Gill on Matthew 21:25).