Matthew 21:34

And when the season of the fruits drew near, he sent his servants to the husbandmen, to receive his fruits.

There were numerous prophets who came again and again, to arouse in Israel the truly spiritual response which the Father desired and which it was impossible for the Law to produce. No age is devoid of such a requirement; but there were some occasions when, it seems God especially desired a quickened conscience in Israel. To be sure, the Law brought forth fruit of a kind, such as outward observance of ceremonial duties and avoidance of some of the grosser sins; but the inner desire and soul-longing for redemptive forgiveness was a fruit God sought in vain in Israel.

As the season ... drew near likely refers, at least in part, to the approach of the times of the Messiah, in which case John the Baptist would surely be among the more honorable servants who came to receive God's fruits from Israel, but who, like the others, was rejected.