Definitely the sacrifice of the Cross was one for all times. However, it does not mean that it applies to everyone based on a mere profession of faith (Matthew 7:21). Were it so, there would be no Sermon on the Mount, no discourse on works-based judgement in Matthew 25, no exhortations to virtue with which St. Paul finishes his every letter, no demand for obedience and total submission to the will of Christ that we have in every Gospel (for example, Luke 18:22), no call to prayer (Matthew 5:44), forgiveness (Mark 11:26), conversion (Luke 13:3) and frequent (1 Cor. 11:25-26) reception of the Eucharist (John 6:54). These are exhortations repeated often, not isolated open to interpretation verses. Christ did put you on the road of salvation, but quite a bit of continuing work is required of you to walk it.
I think that working on Freedom TO might be useful in getting a sense or flavor of Catholic Thought as it touches works and stuff.
WE are saved not only FROM perdition, and even though most if not all of us waver, we find one good work given to us in our saving a work we are freed TO, a new impulse and ability to be grateful to God. We are Saved TO Eucharist, in all senses of the word. Can we all agree on that?
IF we can, then by your courtesy, entertain this: that not only that Good work, that of giving God the praise and thanks he is Due, is offered to us, but other good works as well. They're not burdens or hoops to jump through. They're gifts. He doesn't carry us across the high places. FIRST He makes our feet like hinds feet THEN he makes us tread on our high places. (Habakkuk 3:19, for those keeping score at home.)