Ibn Ezra on Leviticus 4:3

לאשמת העם. שהורה שלא כהוגן ואשם העם וכלם שוגגים או פירוש לאשמת העם באשמת כל בני אדם ונזכר כן בעבור שהכהן הוא נושא התורה והוא עצמו נשמר וקדוש לשם: TO BRING GUILT ON THE PEOPLE. The kohen gadol taught incorrectly and the people were guilty, all of them having acted inadvertently.⁷The people inadvertently sinned by following the wrong ruling of the kohen gadol. On the other hand, the meaning of leashmat ha-am (to bring guilt on the people) might be, because of the guilt of all of the people.⁸The kohen gadol is responsible for the people’s sin. He did not sufficiently admonish the people. It⁹The phrase le-ashmat ha-am (to bring guilt on the people). According to this interpretation our verse reads: If the appointed priest shall sin because of the people’s guilt. is mentioned here¹⁰After the word yechete (shall sin). In other words, le-ashmat ha-am (to bring guilt on the people) qualifies yechete (shall sin). because the kohen is the bearer of the Torah and he is very careful and holy unto God.¹¹He himself would not sin inadvertently.

על חטאתו. בעבור חטאתו וכאשר הוא גדול יקריב הפר שהוא הגדול מכל הקרבים על גבי המזבח: FOR HIS SIN. Al chattato (for his sin) means because of his sin.¹²Al chattato (for his sin) literally means on his sin. Hence I.E.’s comment. Since the kohen gadol is great he must offer a bullock, which is the largest animal of all that are offered on the altar.