Language usage changes over time. This text seems to come from the 17th or 18th Century. I assume that you are questioning "abundant of reason". Here, it means full of reason. A shorter, and more modern way to express this thought would be "reasonable", though it lacks some of the power given by "abundant". I have a book of Shakespeare's plays. On some pages one-third of the page is original text and two-thirds are footnotes explaining the first one-third. It is interesting to be able to read a text in its original form, and to understand it. Problems start when you attempt to use phrases that are no longer in use or which have been changed over time.
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