Numbers 19:5

And [one] shall burn the heifer in his sight
Another priest, as the Targum of Jonathan, Eleazar looking on, as that expresses it; the Jews say ^F7, that when the priest came to the mount of Olives, accompanied by the elders of Israel, before he burnt the cow, he dipped himself in a dipping place there; and the wood being laid there in order, wood of cedar, ash, fir, and fig trees, made in the form of a tower, with holes opened in it (to put in the fire, and that it might burn the quicker), and its aspect being to the west, he bound the cow, and laid her upon the pile, with her head to the south, and her face to the west; and then having slain it, and sprinkled its blood, as before related, he set fire to it by the help of some small wood: the burning of it may signify the dolorous sufferings of Christ, when the wrath of God was poured forth like fire upon him; the same was signified by roasting the passover lamb:

her skin, and her flesh, and her blood, with her dung, shall he burn;
which may denote the extent of Christ's sufferings, reaching to all parts of his body, skin, flesh, and blood, and the shame and reproach that attended them, signified by dung; as well as how impure and accursed he was accounted when he was made sin for his people, bore their sins and suffered for them, even not in body only, but in his soul also; for his soul as well as his body were made an offering for sin.