Servant - i. e., A slave, whose obedience is reluctant. He may “understand” the words, but they produce no good effect. There is still lacking the true “answer” of obedience.
SDA Bible Commentary (limited)
Volume 1-7
19. Will not answer. That is, he will not respond to instructions. Although the reluctant slave understands well what his master wants him to do, it will take more than words to make him do it.