Sola fide ("by faith alone")
It means "only faith" and it excludes the good works as necessary for salvation. Sola fide is the teaching that justification(interpreted in Protestant theology as "being declared just by God") is received by faith only, without any mixture of or need for good works,
The Sola fide doctrine is sometimes called the material cause or principle of the Reformation because it was the central doctrinal issue for Martin Luther and the other reformers. Luther called it the "doctrine by which the church stands or falls.