Or HaChaim on Leviticus 9:3/אור החיים על ויקרא ט׳:ג׳

1 תדבר לאמור, "you shall speak saying;" We need to explore the reason why Moses commanded Aaron to speak in this instance instead of instructing the Israelites himself as was his custom. Perhaps it was because at the time of the golden calf it had been Aaron who invited the people to bring him their gold, Moses now wanted to give him an opportunity to speak to the people and tell them to bring a male goat to be the sin-offering as atonement. This would be in line with the principle הפה שאסר הוא הפה שהתיר, "that the mouth which uttered the prohibition must be the mouth which utters the permission." We have repeatedly quoted our sages as saying that the sin which causes someone's reputation to become sullied can best be repaired when the method of rehabilitation is as closely linked to the circumstances of the sin it rehabilitates as is possible. This is why G'd ordered Aaron to inform the people of this procedure. The words תדבר לאמור mean that inasmuch as on the previous occasion Aaron had uttered words which resulted in the people becoming unrestrained, demeaning themselves, he was now to utter words which would eventually elevate the people and result in atonement for that sin.

2Furthermore, seeing that Moses had observed how Aaron had been elevated by G'd to such a high position, Moses told him to communicate soothing messages to the Jewish people. The word לאמור implies a message couched in a very friendly manner. Aaron told the people that G'd would appear to them (verse 4) to indicate that the whole procedure he was instructing them about was for their good, not for his own. This recalls what we wrote in the name of Torat Kohanim at the beginning of פרשת ויקרא, that the fact G'd did not communicate with Moses in the Tabernacle for 38 years was on account of the sin of the spies; when G'd is reported as communicating with Moses out of the Tabernacle this was a compliment to Israel.