II.1 chapter 31

The seventh day signifies the rest of God. Of the seventh day the evening is not mentioned: God does not have the knowledge 'of the night' like the creatures but only the knowledge 'of the day'. The number seven is often used to signify all numbers together (it is composed of the first odd number three and the even number four) and thus the completeness and generality of anything. In partiality there is labour, but in completeness is rest.
(Likewise in our partial knowledge we desire for the perfection which will put away all effort, like it is with the holy angels already.)

II.1 chapter 30

Are the works of God (which came forth from the unchangeable Word of God) an imperfect reality?
No, they are still a perfect reality. This is signified by the number of days in which the world was made: in six days, where the number six is the first perfect number (perfect numbers are sparse: following are 28, 496, 8128, 33550336, ...).

(And therefore we must not despise the science of numbers, which, in many passages of holy Scripture, is found to be of eminent service to the careful interpreter.)

II.1 chapter 29

There is a difference between the knowledge through the Word of God and knowledge through the appearance of things, like it is different to know a mathematical figure by definition and to know it by figure. It is for example different to know justice by the unchangeable truth and to know it by the 'figures' in the human soul; it is different to know the physical things by their causes and reasons and to know it by their art or work. The first compared to the second is as day compared to night (see chapter 7 of this book).

[Compare the notion of 'idea', which form the unchanging basis of what we encounter, at Plato.]