Leviticus 23:44

And Mosheh declared the time of the orders of the Lord's festivals, and taught them to the sons of Israel.

to the children of Israel not literally to all the children of Israel, since he could not possibly speak to all of them. The same applies whenever the phrase “speak to the children of Israel” appears. The verse “the entire assembly of the children of Israel” [19:2] poses no problem, since the term “assembly” does not denote the entire nation.

AND MOSES DECLARED UNTO THE CHILDREN OF ISRAEL THE APPOINTED SEASONS OF THE ETERNAL. The meaning thereof is as follows: The above sections contain admonitions directed to Aaron and his sons, and Moses therefore told them to Aaron and his sons, and sometimes He mentions after them also the children of Israel, as He said at the end of the section dealing with blemishes, So Moses spoke unto Aaron, and to his sons, and unto all the children of Israel, for although Moses was only commanded, Speak unto Aaron, saying, Whosoever be of thy seed,, Verse 17. he wanted to exhort the court of Israel about this matter [and therefore he also spoke to all the children of Israel]. Perhaps the reason [why he exhorted the court] is because a person covers up his blemishes, and the priest does not want to be disqualified on account of them from performing the Divine Service, for it is a [source of] shame and disgrace, therefore He exhorted the court about this matter. But here Scripture states that he declared the appointed seasons of the Eternal to all the children of Israel as one man, and it did not single out the sons of Aaron in these commandments, the reason being that the admonition applies to all alike, since the main [commandments] of these sections are that we are to rest on the Sabbaths and festivals, and to proclaim them holy convocations. None of the offerings are mentioned in these sections, except for the offering of the sheaf [on the second day of Passover], and the two loaves [on the Festival of Weeks], as they [these festivals] are the causes for their being offered. And in the section where the main offerings of the Day of Atonement are set forth,, Chapter 16. it says, Speak unto Aaron thy brother. Verse 2. [because it was Aaron’s duty to perform the Service on that day].
And our Rabbis have interpreted [the verse before us] as follows: 17:12. “And Moses declared unto the children of Israel the appointed seasons of the Eternal. This teaches that Moses told Israel the laws of Passover on the Passover, and the laws of Atzereth [the Festival of Weeks] on Atzereth, and the laws of the Festival of Tabernacles on Tabernacles. In the very language that he heard it, in that language he told them all the sections.” Onkelos also intended to imply this point, for he rendered the verse as follows: “And Moses declared the order of the appointed seasons of the Eternal, and taught them to the children of Israel.” It appears [from Onkelos’ additional phrase “the order of “] that his opinion is to allude [to the fact] that Moses taught the children of Israel the order of the festivals by means of the intercalation [of the years with an extra month], which was handed over to him by word of mouth on Sinai, this being alluded to in the Scriptural text, which ye shall proclaim holy convocations, and Moses taught the children of Israel by word of mouth the whole traditional order of the secret of intercalation.