A number of people have read this text and concluded that it teaches a true believer can apostatize and lose or forfeit his/her salvation. Is that what it really says?
We must first ask the question: were Hymenaeus and Alexander saved? It's difficult to say. There is no way of knowing whether their presence in the church at Ephesus was an external association based on their verbal profession of faith or an internal, spiritual union with the body of Christ. We are told that they 'rejected' a 'good conscience' and as a result suffered "shipwreck in regard to the faith" (v. 19). As Stott has said, "if we disregard the voice of conscience, allowing sin to remain unconfessed and unforsaken, our faith will not long survive" (57).
Paul took disciplinary action by delivering them 'over to Satan'. His purpose in doing so was in order that 'they may be taught not to blaspheme' (v. 20). Were they Christians? Certainly believers are capable of backsliding and doing serious damage to their fellowship and intimacy with Christ. Believers are capable of falling into serious doctrinal error and are subject to being excommunicated. The imagery of a "shipwreck" suggests serious damage but need not imply, and certainly does not require, the notion of a loss of salvation. The pedagogical purpose in Paul's action, to teach them not to blaspheme, would be consistent with how a believer who had fallen into doctrinal error should be viewed. Paul's disciplinary action would thus have as its purpose the restoration of a wayward brother.
On the other hand, they may well have been non-believers from the beginning. In rejecting a good conscience they made shipwreck of, literally, 'the' faith, i.e., the truths of Christianity objectively considered. That is to say, this may be a description of their willful abandonment or repudiation of the truth of the gospel, resulting in their expulsion from the church. The theological bottom line, however, is that nothing in the passage demands that we conclude these men were born-again believers who lost their salvation.