Soli Deo Gloria

The “solas” strike at the heart of the differences between Rome and Reformed churches.

Grace Alone
Rome states that salvation is by grace [...] plus man’s effort.  The traditional Roman Catholic formulation is, “God will not deny his grace to those who do what is in their power.”  In more modern terms, “God helps those who help themselves.” [...] By contrast, the Reformed churches state that salvation is by grace alone [...] It is only and entirely by God’s grace that man is saved.

Faith Alone
[...] Rome has explicitly denied that justification is by faith alone and in fact condemns Reformed believers who hold to this position [...]  Moreover, according to Rome, justification is a life-long process by which we are made righteous, rather than a one-time event where we are declared righteous. [...] Finally, faith is also redefined by Rome to include good works and these good works become part of the meritorious basis of justification. [...T]he Reformed churches state that justification is by faith alone (Romans 3-4).  God declares us righteous (a one-time event) [...]

Christ Alone
[Rome states] it is not Christ alone when it comes to justification.  Instead, it is Christ plus [...] "If anyone says that justice once received is neither preserved nor increased in the sight of God by good works, but that the works themselves are no more than the effects and signs of justification obtained, and not also a cause of its increase, let him be anathema" (Trent, session 6, canon 24). The Reformed churches argued that [...] Christ alone is the basis for our justification — he lived a perfect life of obedience for us and in our place.  He died once for all on the cross for us and in our place.  God imputes all his merits to us, and all our sin has been imputed to him and thus we are accounted righteous before God.

Scripture Alone
[F]or Rome, it is Scripture plus tradition. [...] The Reformed churches retorted that only the Bible can be our ultimate authority and we may not add or take away as we please [...] Yes, we ought to give heed to the early church fathers, councils, synods, etc.  In fact, the writings of the Reformers are filled with references to these.  But because these are all made up of men, they can and have erred.  Thus, everything is to be scrutinized with the infallible and inerrant Scripture, which is the norming norm.

The Glory of God Alone
[...] Rome states that God is to be worshiped and glorified.  Yet, Rome also promotes the worship of Mary and the saints, giving glory to human beings.  The “Hail, Mary” and “Hail, Holy Queen” prayers on the rosary would be enough to prove this, and much more could be added. The Reformed have always said, “Soli Deo Gloria,” “To God Alone the Glory.” 

~"Letter to a Friend," by Wes Bredenhof