Sentence:  Thus human nature seems to lie under the disadvantage, that the example alone of a vicious prince, will in time corrupt an age; but the example of a good one, will not be sufficient to <WSD>reform</WSD> it without farther endeavours. 
Meaning of the word marked with <WSD> tags:  To put into a new and improved form or condition; to restore to a former good state, or bring from bad to good; to change from worse to better