There is a tendency on either theological side of the issue of eternal security to exaggerate the other’s position. I have heard many preachers say that people who believe you can forfeit your salvation believe that if you sin in the least you are in danger of hell, and therefore have no assurance in their faith at all. This is not the case. This perception isn’t any more true than that of the Arminianist who claims that the Calvinist believes you can be saved and sin all you want and still go to heaven. This is the extreme being exaggerated on the other side.
Allow me to use an illustration to show what I mean when I say we believe that the Christian can forfeit their salvation. An important thing to note here is that we use the word forfeit instead of the word lose. Suppose someone puts a five dollar bill in their pocket and walks to the store, but when they reach the cashier to make their purchase they find that the five dollar bill is no longer in their pocket. They have lost it – it must have fallen out along the way, unbeknownst to its owner. This is what we don’t mean when we say one can forfeit their salvation, and why we chose the word forfeit over the word lose.
To lose one’s salvation would be like the person in the illustration losing their money – it would happen by accident and without the person knowing what happened. Suppose however, that the person gives the money away to somebody. They could have given it away out of anger to a sibling who was pestering them; or maybe they gave it to a friend; or maybe they had so much money that they threw it on the ground, thinking that they didn’t need it anymore. The method doesn’t matter; the point is that the person forfeited their money out of a conscious act of the will. Afterward, they cannot expect to go to the store and purchase what they had intended with that five dollars, because they no longer have possession of it. They have consciously given it up, for whatever reason.
Likewise, someone is very capable of walking away from their faith in the Lord Jesus Christ, and consequently from the salvation that he gives. Just as by a conscious act you receive your salvation, by a conscious act you may also tell God that you don’t want it anymore. To use another illustration, salvation is like a present given: you can chose to say you don’t want it and give it back to the person who gave it to you.