In 2 Peter 1, Peter writes:
His divine power has granted to us all things that pertain to life and godliness, through the knowledge of him who called us to his own glory and excellence, 4 by which he has granted to us his precious and very great promises, so that through them you may become partakers of the divine nature, having escaped from the corruption that is in the world because of sinful desire.
Whatever he means by “nature,” he does not mean “substance” or “essence.” If he did, that would mean that Christians are homousios with the Father, Son, and Holy Spirit, which would in turn make Christians polytheists. And presumably no one wants to affirm that.
Girolamo Zanchi explains in two sections of the second chapter of De religione Christiana fides, entitled De Deo, divinisque personis et proprietatibus (“On God, and on the Divine Persons and Properties”). After stating that the Persons are distinguished by their personal properties (unbegottenness, begottenness, procession), but that they in turn differ from all creatures with respect to the essential properties, he writes:
IIII: That in God, the essential properties in fact do not differ from the essence.
For we recognize that in God, on account of his simplicity, the essential properties do not in fact differ from the essence; and that, consequently, they are not able to be communicated to any creature without it; and that, for that reason, no creature truly is, or is able to be called, simply omnipotent (for example), simply good, just, wise, and other things of this kind, just as the Lord Jesus too, though speaking about only one attribute, taught about them all, when he said, “No one is good (simply) but God.”
V: That nothing is or is able to become simply what God is, unless it is also able to be God simply.
Therefore, it is necessary that those who wish for it to have been possible or to be possible for any created substance to become a partaker of the divine properties, by which it would be what God also is (as simply omnipotent, and things of this kind), to confess that this [created substance] is or is able to be homoousios with God, since not even the Son himself is simply omnipotent, except because he is homoousios with the Father; and so also the Holy Spirit [is omnipotent in this way]. 1