Faith is the assurance of things hoped for and the conviction of things not seen (Hebrews 11:1.) it stands in reason that it is in Luther’s Solas, as it is a doctrinal foundation for our whole ‘faith.’ Sola fides means ‘justified by faith alone,’ and biblically speaking I think it is a strong and true statement, there is nothing we can do to save ourselves, besides having faith in Christ’s work. Faith is simply the method in which we receive God’s salvation. It is faith that lets us receive the gospel, and through His gospel, His righteousness. Faith is unique in this; it is the vehicle that we use to receive God’s gift. It’s just about what God has done for us. Turn to Romans 3:21…
 But now the righteousness of God has been manifested apart from the law, although the Law and the Prophets bear witness to it— the righteousness of God through faith in Jesus Christ for all who believe. For there is no distinction:  for all have sinned and fall short of the glory of God,  and are justified by his grace as a gift, through the redemption that is in Christ Jesus,  whom God put forward as a propitiation by his blood, to be received by faith. This was to show God’s righteousness, because in his divine forbearance he had passed over former sins.  It was to show his righteousness at the present time, so that he might be just and the justifier of the one who has faith in Jesus.
 Then what becomes of our boasting? It is excluded. By what kind of law, by a law of works? No, but by the law of faith.  For we hold that one is justified by faith apart from works of the law.  Or is God the God of Jews only? Is he not the God of Gentiles also? Yes, of Gentiles also,  since God is one—who will justify the circumcised by faith and the uncircumcised through faith.  Do we then overthrow the law by this faith? By no means! On the contrary, we uphold the law. (Romans 3:21-31 ESV)
God brings righteousness ‘through’ faith. Can you not see the power in this? Through the vehicle of faith, righteousness can be ours in Christ, and by ‘ours,’ I mean anyone! Faith is the great equalizer there isn’t a distinction in race or culture, faith isn’t given more or less based on anything besides God’s grace! It is by ‘faith’ that we can believe and receive Christ as our justifier and propitiation, as our redeemer and sacrifice. And through faith, he might be that justifier for us.
God has always been saving people in the same way, through FAITH. In Romans 4:3 Paul states, “Abraham believed in God and it was accounted to him as righteousness,” then he says “the one who works, will be given their wage, but not a gift. But the one who believes in him who justifies the ungodly, HIS FAITH WILL BE COUNTED AS RIGHTEOUSNESS.” However it is not just faith in itself that saves us. But It is faith in something, that something being Jesus’ work.