This article, from En-Gedi, is the sort that gets you in trouble with the TR crowd(Truly Reformed - those who try to outdo each other in how Reformed and confessional they are) - I think it is right on, though, in pointing us to James (2:14-26) to see what kind of faith it is that alone justifies us.
Faith and Faithfulness
Abram believed the Lord, and he credited it to him as righteousness. Gen 15:6
One of the most quoted verses about Abraham is Genesis 15:6. This is a key verse that is used in the discussion about being saved by faith apart from works — the central point of the Protestant Reformation. It was Abram's "believing" that gave him righteousness in God's sight. From this verse, Christians historically have emphasized the importance of believing God's promises, instead of working to earn our salvation.
But it is important to understand that the key word, emunah, which we translate "believe," has a different emphasis in Hebrew than we tend to hear. In English and in Greek (pistis), its primary meaning is to assent to a factual statement, to agree with the truth of certain ideas.
The word emunah does mean “to have faith,” but it has a broader meaning that has implications for what God calls us to as people of faith. It also contains the idea of steadfastness or persistence. Exodus 17 tells us that Moses raised his hands all day long until the Israelites won a key battle. It says that his hands remained steady (emunah) until sunset. In this sense the word means “steadfast.”
The word emunah is also used to describe God’s faithfulness:
Know therefore that the Lord your God is God; he is the faithful (emunah) God, keeping his covenant of love to a thousand generations of those who love him and keep his commands. (Deuteronomy 7:9)
If we look back at the verse about Abraham's emunah, it should tell us that Abraham believed God's promises and had a persistent commitment to God, which was displayed in his faithful life — waiting 25 years for a son, and then offering him back to God when he was asked to do so.
This has implications about what it means to be a Christian. I used to wonder why God saved certain people just because they decided to adopt one particular set of beliefs over another. But as James pointed out, Satan himself believes the truth about God and Jesus (James 2:19); and just knowing that doesn't redeem him! But while Satan may have the right beliefs, he cannot say that he has emunah — a committed faithfulness to the Lord. What God asks for goes beyond an academic decision to believe that a certain set of facts are true. He wants faith in his promises that results in steadfast faithfulness to him.
by Lois Tverberg