"Protestants and Catholics agree that faith is necessary for salvation. The Bible clearly teaches that it is. Good works alone do not merit salvation. No one can "buy" heaven with enough good works, or good enough motives. The ticket to heaven is not being nice or sincere or good enough; the ticket to heaven is the Blood of Christ, and faith is the acceptance of that free gift. But the Church insists that good works are necessary too. This means the works of love. Good works are not mere external deeds, but the works of love. And love is not mere feelings, but the works of love (charity, agape). That is why Christ can command them; feelings cannot be commanded.St. James clearly teaches that "faith by itself, if it has no works, is dead" (Jas 2:17). And some of Christ's parables teach that our salvation depends on our charity (Mt 25:40: "as you did it to one of the least of these my brethren, you did it to me"). St. John of the Cross wrote: "At the evening of life, we shall be judged on our love".It is not that we purchase heaven with our good works; Christ has already purchased heaven for us with his work of love on the Cross. We do not do good works to get to heaven, but we do good works because heaven has gotten to us. If we do not do good works, that shows that heaven has not gotten to us. For "you will know them by their fruits" (Mt 7:20)...Luther thought forgiveness was only external and legal ("forensic"). Catholic theology teaches that it actually changes our souls." - Catholic Christianity p.126
Very different from the Protestant idea, but I think Kreeft has a way of making Roman Theology sound appealing whereas many others make it sound repulsive.