Sforno on Leviticus 4:3/ספורנו על ויקרא ד׳:ג׳

1seeing that sinners are always on different levels morally and ethically, some being more prone to sin than others, the Torah addresses these different groups of people in different ways, each one appropriate to their specific rating in society. The Torah begins with the High Priest, the one who is least likely to commit a sin, and writes: אם הכהן המשיח יחטא לאשמת העם, implying that a sin by the High Priest is most likely the outcome of guilt by the people, their conduct having contributed to his committing such an error. The Talmud (Berachot 34b:29) quotes that if someone makes an error in his private prayer this is a bad omen for him. If, however, the cantor, i.e. the person hired to pray on behalf of the people makes an error, not only he but all those on whose behalf he offered his prayers will suffer the consequences of his error. The sacrifice of a priest who committed an error must be burned and no one derives the slightest benefit from such an offering. Such considerations account for the fact that the Torah did not write here ואשם, “he sinned,” which would have been a warning for the errant person to do teshuvah. Had the Torah phrased its address to the High Priest thus this would not have been appropriate as the error committed by the High Priest did not originate within his heart but his faulty prayer had been due to the sinfulness of the people he represented which had insidiously influenced the words he was uttering.