No further revelation is given. Jesus Christ has spoken all that is necessary through His apostles in the Bible. Salvation is by grace alone. God is never under any obligation to grant salvation. If God's justice required that He give grace to all men, then salvation would not be a gift but an act of justice.
Salvation is through faith alone.
Rather than being declared righteous on the basis of our faith plus our deeds, we are declared righteous solely on the basis of our faith in Jesus Christ. By faith, Christ's righteousness is imputed to the sinner not infused or imparted. The sinner does not become righteous at salvation but is judicially declared righteous on account of Christ's righteousness. We are justified by faith alone but not by faith that is alone. Salvation is because of Christ alone.