As Dottard mentioned James 2: 14- 26 doesn't address this problem. However, one's theology needs to be consistent with this passage along with passages, such as "the one who endures to the end shall be saved (Matt. 10:22; 24:13; Mark:13:13)." In that sense the question becomes academic, unless you discount God's sovereignty and open up what if circumstances, sometimes called straw men arguments.
How can we reconcile the lost faith passages Dottard reference verses passages like?:
Whoever believes in the Son has eternal life; whoever does not obey the Son shall not see life, but the wrath of God remains on him.
(John 3:36, ESV)
Truly, truly, I say to you, whoever hears my word and believes him who sent me has eternal life. He does not come into judgment, but has passed from death to life.
(John 5:24, ESV)
37 All that the Father gives me will come to me, and whoever comes to me I will never cast out. 38 For I have come down from heaven, not to do my own will but the will of him who sent me. 39 And this is the will of him who sent me, that I should lose nothing of all that he has given me, but raise it up on the last day. 40 For this is the will of my Father, that everyone who looks on the Son and believes in him should have eternal life, and I will raise him up on the last day.”
(John 6:37–40, ESV)
No one can come to me unless the Father who sent me draws him. And I will raise him up on the last day. 45 It is written in the Prophets, ‘And they will all be taught by God.’ Everyone who has heard and learned from the Father comes to me— 46 not that anyone has seen the Father except he who is from God; he has seen the Father. 47 Truly, truly, I say to you, whoever believes has eternal life.
(John 6:44–47, ESV)
but you do not believe because you are not among my sheep. 27 My sheep hear my voice, and I know them, and they follow me. 28 I give them eternal life, and they will never perish, and no one will snatch them out of my hand. 29 My Father, who has given them to me, is greater than all, and no one is able to snatch them out of the Father’s hand. 30 I and the Father are one.”
(John 10:26–30, ESV)
You can either develop arguments to counter those on the other side, or you can seek to reconcile both. The conflict directly relates to determinism verses free will. This is a much larger problem for science than Christianity, because cause and effect has no room for free will.
Human choice exists because of God's sovereignty, not in conflict with it. The human mind (intellect, volition, and emotion) is evidence for God. A subset of that is the moral argument given for C. S. Lewis. In God's sovereignty he knows who will be saved and and knowing can take them away. Our inability to know our individual futures other than what the Bible reveals is essential to a freedom of choice. Thus, it is possible for a person to think they are saved, but end up being lost. Thus, from the human standpoint it is possible to loose faith and fall from grace. So, the important issue is assurance of salvation, which the Scriptures discuss.
I write these things to you who believe in the name of the Son of God, that you may know that you have eternal life. 14 And this is the confidence that we have toward him, that if we ask anything according to his will he hears us. 15 And if we know that he hears us in whatever we ask, we know that we have the requests that we have asked of him.
(1 John 5:13–15, ESV)