For those whom God foreknew, he also predestined to be conformed to the image of His Son, that He might be the firstborn among many brethren. Moreover, those whom He predestined, He also called; and those whom He called, he also justified; and those whom He justified, He also glorified.This 'foreknew' is not a foreknowledge of what free agents will choose, as though God takes in knowledge of events, outside of his decree, that from His perspective could have been otherwise. It is an active, personal knowing. To illustrate the distinction, Spanish (and I presume many other languages) has a distinction between two kinds of knowing: saber, which means to know about stuff; and conocer, which means to have intimate experience with people and/or stuff. (And I believe conocer is a cognate of the greek ginosko, which is part of the word translated foreknow--proginosko). Paul is talking about an active knowing of a specific people ('those whom...'), and there is no indication of any qualification on their part. That is, despite the classic Arminian interpretation, it doesn't say, "Those whom God foreknew would accept Christ." To beat this dead horse, it is not that God foreknew something about certain people; God foreknew these people.
This is one of the clear passages in Scripture regarding the security of the believer, against which all warning passages that might cast doubt on our security must be judged and interpreted.
The other question is, "What about those whom God did not foreknow?" As a believer in Universal Reconciliation, I yet believe there is a predestined Elect in this age, and the purpose for this election is succinctly and brilliantly (thank you, Holy Spirit) stated by Paul, in Ephesians 2:7:
That in the ages to come he might shew the exceeding riches of his grace in his kindness toward us through Christ Jesus.