Gospel Guidebook: Getting and Keeping It Right 
Faith is NOT a Choice
There are many people who think that saving faith is a choice because God commands us to believe. However, the command to believe simply points us to what needs to be done. But what needs to be done leaves no room for choice. Saving faith refers to being persuaded by the evidence of the Gospel. You are either persuaded by it or you aren't. There is no choice in the matter. If faith is a choice, then faith saves. If faith is a persuasion, then the object of faith saves. This is the difference between appropriation (which in itself is a subtle form of works salvation, and even more so when coupled with choice) and grace. However, if we really believe that Christ did it all, then we know that we don't appropriate anything, but rather, Christ confers His salvation upon us and faith is simply His way of having us recognize it.
Justification occurs irreversibly upon a single moment of faith. Because of this, we might be tempted to make too much of the moment of faith, as if it was faith itself that saved us. When Jesus told people that their faith saved them or when the Scripture says that Abraham's faith was imputed to him for righteousness, we have to realize that faith represents its object. This is why Jesus said to the blind men, "Do you believe that I can do this?" (emphasis added). It's the object of faith that matters. The blind men didn't save themselves. Jesus saved them. There is nothing inherently good about faith. Faith is nothing more than the persuasion of the mind that something is true. In many instances, the object of a person's faith, instead of saving them, can actually destroy them. For example, people who believe in a false god are harmed by the object of their faith. People who believe in money are deceived by the object of their faith. In these instances, the problem doesn't lie in faith itself, but the object of their faith. In the case of justification, faith is the persuasion that the content of the Gospel is true, by which we recognize that Jesus did it all. But if this is the case, then there is no room for choosing or appropriating anything.
When someone believes the Gospel, assurance is of the essence of faith. However, assurance is only possible to the extent that such a person is currently believing the Gospel. For example, if such a person believed the Gospel and was justified by faith years ago, but then fell away from the faith for a while, his justification remains valid, but he doesn't enjoy the assurance of salvation until he believes the Gospel afresh. If he were to look back to his moment of faith for assurance, he would not be believing the Gospel, but would be believing faith. It is a big mistake to get assurance from faith itself or think that we have favor with God because we supposedly made a choice to accept Jesus so many years ago. Instead, our assurance must come from believing the Gospel. The Gospel is our only source of assurance.