Sforno on Genesis 1:31/ספורנו על בראשית א׳:ל״א

1את כל אשר עשה והנה טוב מאד, the accomplishment of a project containing many different parts is greater than the accomplishment of each part of such project successfully. Now that G’d had completed the entire project successfully, the Torah described this with the additional word מאד instead of merely טוב.

2יום הששי, this is the first day which is described as “the (sixth) day.” In other words, it was the first of many days known as “the sixth,” but this was the first such day. The specific function of the sixth day is to be the bridge between the ordinary weekdays and the Sabbath. The “six” days have been defined in Exodus 20,9-10 as the days on which “you will perform all your tasks involving work.”