Jamieson, Fausset and Brown on Numbers 29:35-40

35-40. On the eighth day ye shall have a solemn assembly--The feast of tabernacles was brought to a close on the eighth day, which was the great day (Joh 7:37). Besides the common routine sacrifices, there were special offerings appointed for that day though these were fewer than on any of the preceding days; and there were also, as was natural on that occasion when vast multitudes were convened for a solemn religious purpose, many spontaneous gifts and services, so that there was full scope for the exercise of a devout spirit in the people, both for their obedience to the statutory offerings, and by the presentation of those which were made by free will or in consequence of vows.