Sentence:  The Nationall Assembly of this Kirk, from which we have our Commission, did promise in their thanksgiving for the many favours expressed in Your Majesties Letter, their best endeavours to keep the people under their charge, in unity and peace, and in loyalty and obedience to Your Majestie and Your Laws, which we confesse is a duty well <WSD>beseeming</WSD> the preachers of the Gospel ... 
Meaning of the word marked with <WSD> tags:  "Without any qualifying word": to be appropriate or creditable.