Question: Why do you call Christ the only way to salvation?
Answer: Because He alone is the Mediator of the covenant and the reconciliation by which humanity is reunited with God the Lord, the well-spring and origin of all salvation. This is explained by St. Paul in 1 Timothy 2:5 and by St. John in 1 John 1:3 “That which we have seen and heard we declare to you, that you also may have fellowship with us; and our fellowship is with the Father and with His Son Jesus Christ.” See also 1 Corinthians 1:30.
5 For there is one God, and one mediator also between God and men, the man Christ Jesus, 6 who gave Himself as a ransom for all, the testimony given at the proper time. 1 Timothy 2:5, 6
30 But by His doing you are in Christ Jesus, who became to us wisdom from God, and righteousness and sanctification, and redemption, 31 so that, just as it is written, “Let him who boasts, boast in the Lord.” 1 Corinthians 1:30, 31
Caspar Olevianus, A Firm Foundation, p. 4