The uses of perfect aspect are as follows.
1. normally in SV order, it bounds the start and end of narratives, and is used for most cases of the pluperfect.
2. vav plus perfect in VS order, especially when the subject is expressed, may be an oblique modality, a term I will explain later.
3. vav plus perfect in the 2nd singular or plural in commandments are the required details in carrying out the commandment.
4. in 3rd person, in ritual, it expresses actions that must be completed for the ritual to be acceptable, hurtsah. These are the details according to which one must judge in a k’lal u-prat [u-k’lal] structure.
5. In a separate clause and following the ki or im plus imperfect clause in a tort law, something that has to go to completion before sanctions apply.
6. as part of a parallel structure, the following part of which is in imperfect, in poetry and prophecy.
7. in a separate clause and following an imperfect aspect verb which indicates a future action, indicating something that must go to completion before the future action takes place.
You saw an example of usage #5 in Exodus 22:4.
An example of #7 is Leviticus 9:4.
ד כְּתֹֽנֶת־בַּ֨ד קֹ֜דֶשׁ יִלְבָּ֗שׁ וּמִֽכְנְסֵי־בַד֘ יִהְי֣וּ עַל־בְּשָׂרוֹ֒ וּבְאַבְנֵ֥ט בַּד֙ יַחְגֹּ֔ר וּבְמִצְנֶ֥פֶת בַּ֖ד יִצְנֹ֑ף בִּגְדֵי־קֹ֣דֶשׁ הֵ֔ם וְרָחַ֥ץ בַּמַּ֛יִם אֶת־בְּשָׂר֖וֹ וּלְבֵשָֽׁם:
He [by definition] puts on a holy linen coat, linen trousers are on his flesh, he girds himself with a linen belt, and mitres himself with a linen mitre; these are the holy garments, he washes his flesh in water and puts them on.
The priest has to be wearing this clothing when conducting a ritual: yilbash. BUT before any of that he has to complete the action of washing in water: rachats, then he puts them on l’vesham.
This has been called the perfect used in a future tense but that’s not what it is. Priests getting dressed happens all the time; they don’t sleep in the linen clothing and they don’t wear it while taking out the ashes of a sacrifice beyond the camp for deposit. They have to put it on every time they do a sacrifice. BUT before they do that, they have to completely wash in water.
This is not an issue of cleanliness. He has to put the linen trousers on his skin. He washes to get things off his skin that would intervene between him and the garments. On the Fact-Checking page, I talk about the “cleanness” issue, which is actually a problem of translation that starts with the horrible Septuagint. The idea that hygiene was familiar to the people of the Torah and Mishnah periods is a case of Historian’s Fallacy. Don’t go there.