Requiring anything be added to Sola Fide for salvation, brings trouble to the soul of God's children. The truth that it is faith alone that justifies is arguably the most comforting reality for God's elect. The rule to love God and love the Brethren is a burden that is light, because obedience to it is not required to be saved, and God gives us the power to obey this rule because His love has been poured into our hearts via the Holy Spirit.