For you have been born again, not of perishable seed, but of imperishable,... I Peter 1:23, NIV
There is a wonderful, natural example in the Bible that explains things so well. In fact it is ignored just because of that, by those who have "private agendas" of devilish doctrines, or are just plain ignorant. This is the eternal truths revealed in the birth process.
Try as they might, those who try to tell us that we can be lost after we are saved, cannot say that a baby, once born can be "unborn". So the saying "once saved, always saved" is often expressed as "once born, always born". To me, this settles it.
Now about the sacred and holy subject of "free will", bowed down to and worshipped as the idol that it is. Have you ever heard of a baby choosing to be born, or selecting who will be his father? Birth analogy to the rescue! Even insemination has a Biblical example for us. Natural birth is an example that cannot be reversed, even if the baby grows up and says, like Job, "I wish I had never been born!"
The only way that those who promote the "losing your salvation" idea, and the "free will" fallacy, can escape these Biblical birth truths, is to ignore them.