A follow-up question

Hi, I asked about a phrase before, and I want to ask another question about it. The phrase is "a long obligement...your virtues", from Areopagitica by Milton:

Neither is it in Gods esteeme the diminution of his glory, when honourable things are spoken of good men and worthy Magistrates; which if I now first should begin to doe, after so fair a progresse of your laudable deeds, and such a long obligement upon the whole Realme to your indefatigable virtues, I might be justly reckn'd among the tardiest, and the unwillingest of them that praise yee.

I got an answer (thanks to Alphecca) saying the phrase means that the nation is much grateful for their (parliament members') virtues. Then, I found another text with a footnote for "a long obligement". It says that "the Long Parliament met in November 1640, four years before Milton published this tract." Why do you think they put such a footnote? Is it to emphasise the duration? I mean, to emphasise the realm has been grateful for that many years?