Faith should not slay reason. Reason is the divine director God himself has placed within each of us:
"...it [the soul] does all that the daemon wishes, which Zeus hath given to every man for his guardian and guide, a portion of himself. And this is every man's understanding and reason."
-Marcus Aurelius
"He [Zeus] has assigned to each man a director, his own personal daemon, and committed him to his guardianship; a director whose vigilance no slumbers interrupt, and whom no false reasoning can deceive."
-Epictetus
Plato wrote in the Timaeus:
"God has given to each of us, as his daemon, that kind of soul which is housed in the top of our body and which raises us, seeing that we are not an earthly but a heavenly plant up from earth towards our kindred in the heaven... for it is by suspending our head and root from that region whence the substance of our soul first came that the Divine Power keeps upright our whole body."
Cleanthes beheld Zeus guiding "the universal force, Reason, through all things interfused... Thyself of all the sovran and the source." From this flows "Eternal Reason, which the wicked flee and disregard... Ill fated folk, for would they but obey with understanding heart, from day to day their life were full of blessing, but they turn each to his sin, by folly led astray."
To claim that faith must slay reason, this heavenly daemon, and pretending doing so is a "service to God" is to embrace the very ignorance and folly Cleanthes condemns. It is the path of superstition and zealotry that leads only to the reckless deeds of men whose own hearts lead them to perversity. Plato warns us in the Sophist that "We certainly must contend by every argument against him who does away with knowledge or reason or mind and then makes any dogmatic assertion about anything."
Listen instead to the daemon God appointed in you.
“Everyone who by faith slays reason, the world's biggest monster, renders God a real service, a better service than the religions of all races and all the drudgery of meritorious monks can render.”
Martin Luther.