Eternal Security

Unfortunately the teaching of eternal security is sometimes the source of problems within Christian circles.  Some Christians believe that if you hold to eternal security you are purposely promoting a license to sin.  On the other hand, some Christians believe that if you don't believe in eternal security you have to keep your salvation by works.  Both sides often misrepresent the other and instead of being gracious on this debatable issue (as we are commanded to be in Romans 14:1-12) people accuse each other of being unbiblical.
It is the position of CARM that once a person is saved he cannot lose his salvation.  I place my conviction upon this position because of my study of Scripture.  But I do not claim that if someone is as studious as I am, that he will arrive at the same position.  I recognize that there are godly people on both sides of the argument.  Nevertheless, I must be true to my convictions and in light of repeated attacks upon CARM as a ministry because of this position, I felt it necessary to write a more detailed defense.
Please understand that eternal security is not a license to sin.  The Christian is regenerated.  He is changed from within, being made a new creature (2 Cor. 5:17).  Those who were indwelt by the Holy Spirit will war with their sin and not seek to abide in it.  Those who declare that they are eternally secure and then go out and sin on purpose in any manner they so choose are probably not saved to begin with since this is contradictory to what Scripture teaches.  1 John 2:4 says, "The one who says, “I have come to know Him,” and does not keep His commandments, is a liar, and the truth is not in him."
There are a lot of verses raised by Christians who believe it is possible to lose one's salvation.  I could analyze each one and provide explanations of how they fit together.  But it would not be necessary if we can find Scripture that clearly states that a person cannot lose his salvation.  If found, this would mean that any other scriptures used to teach we can lose our salvation must be interpreted in a manner consistent with the one(s) that clearly say we can't.
I will deal with three sets of scriptures: John 6:37-40; John 10:27-28; 1 John 2:19.