"What does scripture say? 'Abraham took God at his word, and that act of faith was accepted as putting him into a right relationship with God'" (The New Testament: A Translation by William Barclay).
Abraham's "act of faith" was to believe the words of God. Simply, faith is believing what God says. That belief, that faith, is what pleases God, putting us in a position to have a right relationship with Him. A right relationship, even on a human level, must have trust as its foundation.
Abraham's example also shows us that this belief, this faith, is not just intellectual agreement but rather a deep conviction that motivates our core and changes how we think. The evidence of this change is an action. True belief and faith must have action to complete it, or else it is dead and useless faith (James 2:20).
Faith—What Is It?
Justification is the imputing of righteousness. In this case, God accounts righteousness where it does not logically belong. We may describe justification as being aligned with a standard. It is also being legally declared free of guilt. Justification can probably be defined about a half a dozen ways, but in no case is justification salvation.
Salvation is deliverance. That is what the word means, to be delivered. Justification means to be made right. They are two different things altogether. In the biblical sense, salvation does not occur until a person is in his inheritance, in the Kingdom of God.
Even though justification does provide a measure of deliverance, it is only the first step towards a person's complete salvation or deliverance. We are still in the flesh. Even though there is no good reason why we should fail, we can still fail—despite being justified.
John W. Ritenbaugh
The Covenants, Grace, and Law (Part Twenty-Nine)
Other Forerunner Commentary entries containing Romans 4:3: