 These are the ones coming out of the great tribulation. They've washed their robes and made them white in the blood of the Lamb. Our pasts have been washed away by His sacrificial blood. That cleansing has come entirely by His actions of grace. Only His mercy covers us in His presence. But with that gracious mercy, we can come without fear, both into the family of God and onto His throne. Hebrews 4, 15 and 16 expresses that freedom due to God's grace.