(1) And the LORD spoke unto Moses, saying: (2) ‘Speak unto Eleazar the son of Aaron the priest, that he take up the fire-pans out of the burning, and scatter thou the fire yonder; for they are become holy; (3) even the fire-pans of these men who have sinned at the cost of their lives, and let them be made beaten plates for a covering of the altar—for they are become holy, because they were offered before the LORD—that they may be a sign unto the children of Israel.’

It is the fire pans that "have become sacred." They had turned them into service vessels, meaning they could no longer be used for any other purpose. 

I don't understand how the fire pans could have become sanctified by ritual use (as Rashi says), when it was "alien" incense that they offered in them. An outsider who uses a sacred utensil for forbidden worship certainly does not sanctify it. I suppose one could say that these became sanctified because they were doing with them what Moses had instructed them to do. They indeed sacrificed their fire pans to heaven, since they expected God to respond with fire, making those fire pans service utensils that would remain permanently in the Tent of Meeting. But in my view, when God tells Moses (v. 3): they have been used for offering to Adonai, they have become sacred, what God means is: "I have sanctified them when they were offered to me, in order that they serve as a warning to the people of Israel."

We thus find it with the primeval serpent [in the Garden of Eden] which set its eyes on that which was not proper for it; what it sought was not granted to it and what it possessed was taken from it. The Holy One, blessed be He, said: I declared: Let it be king over every animal and beast; but now, Cursed art thou above all cattle and above every beast of the field.¹ I declared, let it walk with an erect posture; but now it shall go upon its belly. I declared: Let its food be the same as that of man; but now it shall eat dust. It said: I will kill Adam and marry Eve; but now, I will put enmity between thee and the woman, and between thy seed and her seed.² Similarly do we find it with Cain, Korah, Balaam, Doeg, Ahitophel, Gehazi, Absalom, Adonijah, Uzziah and Haman, who set their eyes upon that which was not proper for them; what they sought was not granted to them and what they possessed was taken from them.