Pieper (2:518): Faith and the denial of justification by faith cannot exist in the same heart. Error in some other doctrines, for instance, in the doctrine of the Lord’s Supper, may be due to weakness and does not necessarily lead to the loss of faith. But error with regard to justification is in every case fatal. One who in his heart trusts in his own morality, works, etc., in order to obtain forgiveness thereby at once places himself outside the Christian Church. “Christ is become of no effect unto you whosoever of you are justified by the Law; ye are fallen from grace” (Gal. 5:4).^\^
David Maxwell, “Justification in the Early Church,” CJ 44:3.
Gerhard, On Justification, § 16: Furthermore, the entire doctrine of justification is comprised in lucid and marvelous brevity in the apostle’s words: “We are justified freely by His” (God’s) “grace through the redemption which is in Christ Jesus, whom God put forth as propitiation through faith in His blood to declare His” (God’s) “righteousness through the remission of previous sins” (Rom. 3.24–25). Here the following are expressed: the efficient principal cause of justification, which is the grace of God; the meritorious cause, which is the obedience and satisfaction of Christ, our Mediator; the formal cause, which is the forgiveness of sins; the instrumental cause, which is faith; the final cause, which is the declaration of righteousness on God’s part and peace of conscience and eternal life on our part. The apostle treats and explains all of these in greater detail in the following chapters.