The apparent contradiction stems from a misunderstanding of "works," and specifically of what Paul wrote about them. Two passages in particular tend to cause a lot of confusion:
That if thou shalt confess with thy mouth the Lord Jesus, and shalt
believe in thine heart that God hath raised him from the dead, thou
shalt be saved.
Ephesians 2: 8-9
8 For by grace are ye saved through faith; and that not of yourselves: it is the gift of God:
9 Not of works, lest any man should boast.
Some people have taken this to mean that salvation comes by some simple act of claiming faith and that after this, the person is saved and salvation is not affected by a person's works. This is a very bad notion, because of what you get when you take it to its logical conclusion: "I have free license to sin because I'm saved and what I do doesn't matter!"
This isn't a hypothetical problem, either. Here's what Richard Hill, an 18th century Wesleyan theologian, had to say on the subject:
"God sees no sin in believers whatever sin they commit... adultery, incest and murder shall, upon the whole, make me holier on earth and merrier in heaven."
This notion is in direct contradiction to the words of the Savior, especially in the Sermon on the Mount, where he taught that not only do sinful actions put us in spiritual danger, but also sinful thoughts. Of particular interest are his words at the conclusion of the sermon:
Matthew 7: 21-23
21 Not every one that saith unto me, Lord, Lord, shall enter into the kingdom of heaven; but he that doeth the will of my Father which is in heaven.
22 Many will say to me in that day, Lord, Lord, have we not prophesied in thy name? and in thy name have cast out devils? and in thy name done many wonderful works?
23 And then will I profess unto them, I never knew you: depart from me, ye that work iniquity.
In verses 22 and 23, the Savior reaffirms that works of righteousness do not bring salvation if the person's heart is not in the right place and they do not truly know Jesus, but in verse 21, we see what appears to be a direct contradiction of Romans 10: 9.
James 2, which has already been quoted, states that faith without works is dead and cannot bring salvation. Peter warned his readers about misinterpreting Paul and wresting the scriptures to their own destruction. And John, in Revelation, makes it clear that in the resurrection we will all be judged according to our works.
So here we have Jesus himself, and also Peter, James and John, the three most trusted of his apostles, all contradicting the simplistic notion of salvation by faith alone and without works. Faced with this, we must either condemn Paul as a heretic, or seek an alternate interpretation, and I don't particularly think Paul was a heretic.
Let's look at Romans 10: 9 first. Remember that he was writing to Roman Christians, subject to Roman law, which wasn't all that favorable to Christianity at that point, to put it mildly. Being willing to confess belief in Christ with your lips was no simple thing the way it is today; it was exposing yourself to persecution and possibly even death simply for the sake of your religion. That's quite a difficult thing to do, even for someone with a lot of faith!
Then we have the passage from Ephesians, where Paul states that salvation comes from faith and the grace of God, and "not of works, lest any man should boast." Reading the context makes it clear that the works he is talking about are the works of the Law of Moses, through which Jews could find a focus for their faith and obtain salvation before it was fulfilled in Christ. The explanation in verse 9 can be understood in that context by reading Luke 18:
Luke 18: 9-14
9 And he spake this parable unto certain which trusted in themselves that they were righteous, and despised others:
10 Two men went up into the temple to pray; the one a Pharisee, and the other a publican.
11 The Pharisee stood and prayed thus with himself, God, I thank thee,
that I am not as other men are, extortioners, unjust, adulterers, or
even as this publican.
12 I fast twice in the week, I give tithes of all that I possess.
13 And the publican, standing afar off, would not lift up so much as
his eyes unto heaven, but smote upon his breast, saying, God be
merciful to me a sinner.
14 I tell you, this man went down to his house justified rather than
the other: for every one that exalteth himself shall be abased; and he
that humbleth himself shall be exalted.
There were those in Jewish society then, as there have always been and still are in every civilization, who boasted of their piety and outward good works and thought that what they did made them better than others. Paul is making it clear that that attitude will score you zero points with the Lord, that even with good works and acts of righteousness, you are still a sinner and nothing you do can undo your past. Only through God's grace can you find forgiveness for your sins.
So we see that good works do not bring salvation in and of themselves, but also that professions of faith that are not backed up with actual righteous living "is dead, being alone," as James put it. Fiducia is a principle that bridges the gap, basically equivalent to the Savior's exhortation, "if you love me, keep my commandments," or James's explanation that we show our faith by our works. A person with true faith will not simply sit around believing that they believe, but will go out and live the Gospel, doing good works out of love for God and love for their fellow men and striving to come always a little bit closer to fulfilling the ultimate commandment, "Be ye therefore perfect, even as your Father which is in heaven is perfect." (Matthew 5:48)