Catholics describe good works as necessary because God rewards acts of faithfulness (good works) of those already justified with sanctifying grace. Not because of deservedness, but due to God’s loving kindness. In Catholic soteriology, such gifts or blessings from God are not understood to have been given frivolously or needlessly by God, as all of his gifts are for the ultimate purpose of attaining eternal life. We believe that God rewards the faithful with necessary gifts to further enlighten the intellect and strengthen the will in such a way as they contribute to one’s perseverance in faith. If we do not remain stedfast in faith, we fall from grace and are no longer justified. Consequently, in this sense, works of the faithful are necessary for eternal life.
With Protestants, I try to change the polemical wording and explain Catholic soteriology in terms they won’t automatically rail against. For example, I think every Protestant would agree with the Catholic assertion that …
The condign merit of Christ ALONE is that which justifies a sinner and makes him righteous in God’s eyes.
Yet, Protestants (at least some) deny the very notion of congrous merit. Catholic soteriology does not. Congruous merit does not, and cannot make an unjust man, just. Instead, it is the gratuitous reward God gives to those already justified who act faithfully (natural and supernatural blessings for faithfulness, which is our willing cooperation with God’s grace working within us). Even when we cooperate with God’s grace, God is STILL not obliged to sanctify or reward us for that cooperation. It is still a gift, completely gratuitous. However, we believe God does indeed reward the faithful. In fact, God can and does reward some for the faithfulness of others (that’s why we pray for others). It is not owed (as was Christ’s condign merit). Instead, it is given gratuitously, not because of our deservedness, but due to the loving kindness of God. Catholic theology describes condign merit of Christ, as merit properly so-called. The congruous merit of the faithful, Catholic theology describes as pseudo-merit.
Condign merit is like a paycheck for work completed. It is obligatory. There would be a true violation of associative justice if the pay was withheld after the work was performed. This is the way Christ merited grace for mankind at Calvary.
Congrous merit is like a gratuity, or using a military example, a medal awarded for meritorious service. As a member of the USAF, the military owes me a paycheck for my efforts (condign merit), but they never owe me a medal (congruous merit). Yet, it is a matter of distributive justice to give medals to those who perform meritoriously. If they did not, they would not be very nice, but they are not strictly obliged to award medals.
The lack of congrous merit on the part of the just neither adds to nor subtracts from the merit of Christ (which is infinite), which ALONE makes a sinner just. Consequently, congruous merit neither adds to or subtracts from the state of justification for those made righteous by Christ. Christ’s work was infinite. His merit is infinite. Furthermore, the source of grace for congruous merit gifted to the faithful, is the condign merit of Christ alone.
So what good is congruous merit? It does not make us just. However, it is still a supernatural gift from God. It adds to our sanctification, not to our justification. Yet, our increased sanctification better equips the faithful against trials. It helps us to grow in our faith. That’s good. That’s necessary for salvation, especially in times of tribulation. Those of “little faith” are justified. Those of great faith are more likely to be stedfast in their faith. This contributes to the attainment of eternal life!! Yet, the lack of congrous merit is not the same as demerit.
A word about “demerit” … those given the obligation to do good works and do not do so, may be committing a grave sin of omission, which does cause us to lose our justification. In other words, failure to do that which is obligatory in the eyes of God can be a serious evil, and may cause us to fall from a state of grace (become unjustified). In this sense too, good works are necessary for salvation. One who is just, but fails to do an obligatory deed may be committing a damnable sin.