John Calvin on Ephesians 2:5

5. Even when we were dead in sin. These words have the same emphasis as similar expressions in another Epistle.

“For when we were yet without strength, in due time Christ died, for the ungodly. — But God commendeth his love toward us, in that, while we were yet sinners, Christ died for us.” (Romans 5:6,8.)

Whether the words, by grace ye are saved, have been inserted by another hand, I know not; but, as they are perfectly agreeable to the context, I am quite willing to receive them as written by Paul. They show us that he always feels as if he had not sufficiently proclaimed the riches of Divine grace, and accordingly expresses, by a variety of terms, the same truth, that everything connected with our salvation ought to be ascribed to God as its author. And certainly he who duly weighs the ingratitude of men will not complain that this parenthesis is superfluous.