I recently had a facebook friend ask me about some hard to understand passages in scripture, as my response was too long to put in comment form I decided to paste it here on my blog. So, enjoy and if you disagree with me about something that is fine, just please be cordial and christian in your comments.
The parables in Matt. 25 are dealing with the world and particularly the church being unprepared for the final coming of Christ. The first parable tells us that some of the virgins (many old commentators think that this is dealing with the professing church, as a virgin would denote professed purity and singularity of heart to a particular person) had slumbered and had not prepared themselves adequately to meet the bridegroom, while others had fully prepared themselves for his coming. The second has similar implications of some servants who had kept the return of their lord in the forefront of their thinking and resulting actions and others who had for all intents and purposes forgot that the lord would come and demand an answer for his actions. If you are asking how this relates to the doctrine of justification by grace alone through faith alone, we must understand that those whom Christ as justified he will also ensure that they grow in grace and truth. (Gal. 3:3, Phi. 1:6, I Cor. 6:9-11, Jam. 2:17-18) when a person is truly converted God begins a sanctifying process in them, a spiritual washing (Eph. 5:26). Someone who claims to be saved and yet lives a life that shows no care for the things of God, that looks exactly like the rest of the world, that has not experienced victory over besetting sins over a period of time, such a person ought to examine himself to see whether he be in the faith. (II Cor. 13:5) Not to see if one has lost their salvation, but to see if they ever really had it at all.
Concerning Heb. 6:4-6, there is no denying that this as a hard passage of scripture to understand and has been debated by hundreds of theologians over thousands of years. My understanding through study is that it speaks of those who have "tried" Christianity out, never fully trusting in Christ but giving him a "trial period" of sorts, when such ones decide that Christianity is not for them, they are without hope. The venerable Dr. John Gill held to this position as well and gave Cain, Pharaoh, and Judas as examples of such. If they make a mockery of Christ's sacrifice for them and cast it off, how else will they be saved? There is no other name given among men whereby we must be saved, so it is impossible for them to be renewed to repentance as they have already made up their mind they will not submit to Christ's finished work.
Hope this helps in some way, I highly recommend John Gill if you can find any of his commentaries, they are available for free on esword.