They refers to the false teachers, and them to the new converts referred to in the previous verse. The freedom that is promised is not political but spiritual freedom. Many suggestions have been made as to what this freedom refers to, among which are the following:
1. It is freedom from fear of punishment at the end of the world. As verse 3 and chapter 3 indicate, the false teachers seem to have become skeptical regarding judgment in general and about the second coming of Christ in particular. In view of this they no longer believe in the idea of a final judgment.
2. It is freedom from corruption or perishability. This means that the false teachers taught that they and their followers are already beyond the bounds of human mortality. This also connects the idea of freedom with what follows in the verse, where the false teachers are described as “slaves of corruption.”
3. If the false teachers are Gnostics, then the freedom that they are talking about is freedom from the enslavement of powers in the universe that are inferior to God, with the result that people feel they are completely free. However, there is no agreement among scholars that these false teachers are Gnostics.
4. It may be freedom from the law, that is, freedom from any rules and regulations that govern the Christian life. This results in a life completely free of any moral restraints. This relates “freedom” to the attitude of the false teachers, who considered themselves completely free from the law and therefore able to do anything they please, including immorality and debauchery.
Although alternative 4 is the most likely interpretation, translators should, if possible, use a general word for freedom. However, in the case of languages that require an object of freedom, we will need to say, for example, “freedom from rules and regulations.”
These people who promise freedom to others are themselves slaves of corruption. This again is a Hebrew idiom; to be a slave of something is to be so controlled and overcome by that thing that you become helpless and hopeless in the face of it. Corruption is one of the keywords in 2 Peter; it is used also in 1.4 and 2.12 (“destruction”). It can mean moral depravity, and certainly this was true of the false teachers with their moral laxness and their indulgence in immoral acts. But more probably corruption here puts emphasis not so much on moral character as on final and ultimate destruction as a result of sin. Thus Good News Translation “destructive habits” is closer to the meaning than slaves of corruption. Other ways of rendering this are “completely controlled by destructive habits” or “completely controlled by habits that will destroy them.” They themselves is emphatic in the Greek.
Peter reinforces his argument with a popular proverb. Whatever (Good News Translation “anything”) translates a dative form that can be taken as masculine, “to whom,” thus “to whomever one becomes subject.” This fits the origin of the proverb, which stemmed from the practice of slave trading; the slaves are first overcome before they are sold. The masculine also fits the context, since the main subject of the discussion is the false teachers. However, it is perhaps more likely that what we have here is a generic neuter, whatever referring to any force, whether personal or impersonal; thus “to whatever one becomes subject.” Overcomes means “defeats” or “overpowers.” Enslaved translates a passive verb that brings out the idea of taking upon oneself the characteristics of slaves, among which are complete ownership by someone, absence of any rights, absolute obedience and loyalty to owners, and helplessness in overcoming such a degrading condition. The final part of this verse may also be rendered “for a person is completely under the control of anything that has conquered him (or, defeated him).”
Quoted with permission from Arichea, Daniel C. and Nida, Eugene A. A Handbook on The Second Letter from Peter. (UBS Handbook Series). New York: UBS, 1980. For this and other handbooks for translators see here .