Sentence:  Because the canon law (following the civil) did allow such "bastard <WSD>eignè</WSD>" to be legitimate, on the subsequent marriage of his mother: and therefore the laws of England (though they would not admit either the civil or canon law to rule the inheritance of this kingdom, yet) paid such a regard to a person thus peculiarly circumstanced, that, after the land had descended to his issue, they would not unravel the matter again, and suffer his estate to be shaken. 
Meaning of the word marked with <WSD> tags:  eldest; firstborn