Surely it saves in the way Peter means that it saves (like any other obedience to God's commands does). What it does NOT do is impute righteousness to a person. If it did, it would be by works, and grace would no longer be grace.
Righteousness is imputed to a person by faith apart from works. The Catholics have a list of things that you must do in addition to believing in God to have righteousness imputed to you. Abraham did NOTHING to have righteousness imputed to him. Paul says he is the example for how we also will have righteousness imputed to us through faith apart from works.
dogma catholic and divine faith revealed by Christ
109. There is a supernatural intervention of God in the faculties of the soul, which precedes the free act of the will.
110. There is a supernatural influence of God in the faculties of the soul which coincides in time with man’s free act of will.
111. For every salutary act internal supernatural grace of God (gratia elevans) is absolutely necessary.
112. Internal supernatural grace is absolutely necessary for the beginning of faith and of salvation.
113. Without the special help of God the justified cannot persevere to the end in justification.
114. The justified person is not able for his whole life long to avoid all sins, even venial sins,
without the special privilege of the grace of God.
115. Even in the fallen state, man can, by his natural intellectual power, know religious and moral
truths.
116. For the performance of a morally good action Sanctifying Grace is not required.
117. In the state of fallen nature it is morally impossible for man without Supernatural Revelation,
to know easily, with absolute certainty and without admixture of error, all religious and
moral truths of the natural order.
118. Grace cannot be merited by natural works either de condigno or de congruo.
119. God gives all the just sufficient grace (gratia proxime vel remote sufficiens) for the
observation of the Divine Commandments.
120. God, by His Eternal Resolve of Will, has predetermined certain men to eternal blessedness.
121. God, by an Eternal Resolve of His Will, predestines certain men, on account of their foreseen
sins, to eternal rejection.
122. The Human Will remains free under the influence of efficacious grace, which is not
irresistible.
123. There is a grace which is truly sufficient and yet remains inefficacious (gratia vere et mere
sufficiens).
124. The sinner can and must prepare himself by the help of actual grace for the reception of the
grace by which he is justified.
125. The justification of an adult is not possible without Faith.
126. Besides faith, further acts of disposition must be present.
127. Sanctifying grace sanctifies the soul.
128. Sanctifying grace makes the just man a friend of God.
129. Sanctifying grace makes the just man a child of God and gives him a claim to the inheritance
of Heaven.
130. The three Divine or Theological Virtues of Faith, Hope and Charity are infused with
Sanctifying grace.
131. Without special Divine Revelation no one can know with the certainty of faith, if he be in the
state of grace.
132. The degree of justifying grace is not identical in all the just.
133. Grace can be increased by good works.
134. The grace by which we are justified may be lost, and is lost by every grievous [mortal,
serious] sin.
135. By his good works the justified man really acquires a claim to supernatural reward from
God.
136. A just man merits for himself through each good work an increase of sanctifying grace,
eternal life (if he dies in a state of grace) and an increase of heavenly glory.