meaning and function of 使 as in "不如小决使道，不如吾闻而药之也"
the origin is 左傳　襄公三十一年:


  鄭人游于鄉校，以論執政，然明謂子產曰，毀鄉校何如，子產曰，何為，夫人朝夕退而游焉，以議執政之善否，其所善者，吾則行之，其所惡者，吾則改之，是吾師也，若之何毀之，我聞忠善以損怨，不聞作威以防怨，豈不遽止，然猶防川，大決所犯，傷人必多，吾不克救也，不如小決，使道不如，吾聞而藥之也，然明曰，蔑也今而後知吾子之信可事也，小人實不才，若果行此，其鄭國實賴之，豈唯二三臣，仲尼聞是語也，曰，以是觀之，人謂子產不仁，吾不信也。


the punctuation of the above text is, imo, doubtful :(

anyway, the metaphor is:

people's animosity (民怨) is like water flow

a ruler can built a dam to store water, and stop the flow. but, over times, water would overflow, destroy the dam.

so, 子產's method to handle people's animosity is: don't stop it, let small amount of water flow daily; in which no water would collected large enough to destroy the dam.


  大決所犯．傷人必多．吾不克救也．不如小決使道．不如吾聞而藥之也


dam burst (大決) . . .

it would be better to (不如) [let] small amount of (小) [water] flow (決) [pass the dam], as (使) dredge (道 --> 疏導).

it would be better to (不如) [let] me (吾) hear (聞) [people's critic (以論執政) at the school (于鄉校)], and (而) [using such critics] as medicine (藥) to cure the governing (之).

depends on the style of writing, one might interpret "使" differently.

have fun :)