The sage has no fixed mind of his own; he takes the people's heart as his heart.
Tips
history
From 《道德经》 chapter 49 (Laozi): 圣人无常心,以百姓心为心。 One of the foundational statements of Daoist political philosophy - the ruler has no private agenda, only channels the will of the governed. Frequently quoted in modern Chinese political discourse about 'people-centered governance.'
usage
以…为… is a classical pattern meaning 'to take X as Y'. Here: take (the people's heart) as (one's heart).