What does it mean that certain men crept in unawares?
It means certain men secretly infiltrated the congregation without people recognizing them as false teachers. They do not announce themselves or bring obvious poison; they come with credentials and appear sanctioned. God foreknew them, and they are ungodly, turning grace into lasciviousness and denying the Lord.
Les explains that Jude verse 4 says there are certain men, not a lot but enough, who crept in unawares. A false teacher never enters a church or denomination and openly says he is adding poison to the good stuff; he comes in as perfectly sanctioned, with all the credentials, yet he is a false teacher. This warning has been from day one. They crept into the midst of the congregation secretly, without people knowing what they are. God in His foreknowledge knew what they were going to do, and that is why He warns the believer to be careful. They were before of old ordained to this condemnation, God's condemnation. In reality they are ungodly, turning the grace of God into lasciviousness and denying the only Lord God and our Lord Jesus Christ.
For there are certain men crept in unawares, who were before of old ordained to this condemnation, ungodly men, turning the grace of our God into lasciviousness, and denying the only Lord God, and our Lord Jesus Christ.