鄭重

一個鄭重的承諾

a solemn promise

然非皇天所以鄭重降符命之意，故是日天復決其以勉書。

However, (his previous attempt to humbly decline the heavenly mandate) was not what Heaven intended by repeatedly dispatching His auspicious signs. Therefore, on that day Heaven again pronounced His verdict in the form of divine scripts (manufactured by Ai Zhang) encouraging him (to assume the imperial throne).

只是說得忒煞鄭重滯泥，正如世俗所謂山東學究是也。

It's just that (the Gongyang and the Guliang) explain stuff so tediously and in such wearisome way, which is exactly what people mean by the "pedants of the East".

悉可以示汝國中人，使知國家哀汝，故鄭重賜汝好物也。

You may exhibit all of them to the people of your land, so that they may understand that We bestow upon you the treasures in sincerity out of our compassion toward you.