For more resources on this subject, see our earlier article “Catholicism.”
Because of the subjective nature of justification, Catholic theologian Ludwig Ott writes, “The reason for the uncertainty of the state of grace lies in this, that without a special revelation nobody can with certainty of faith know whether or not he has fulfilled all the conditions that are necessary for achieving justification.” Catholic apologist Tim Staples argues that we cannot have absolute certainty of our salvation—anymore than we can be certain of having our prayers answered (1 Jn. 5:14-15). Vatican II explains,
But the task of authentically interpreting the word of God, whether written or handed on, has been entrusted exclusively to the living teaching office of the Church, whose authority is exercised in the name of Jesus Christ. This teaching office is not above the word of God, but serves it, teaching only what has been handed on, listening to it devoutly, guarding it scrupulously and explaining it faithfully in accord with a divine commission and with the help of the Holy Spirit, it draws from this one deposit of faith everything which it presents for belief as divinely revealed. It is clear, therefore, that sacred tradition, Sacred Scripture and the teaching authority of the Church, in accord with God’s most wise design, are so linked and joined together that one cannot stand without the others, and that all together and each in its own way under the action of the one Holy Spirit contribute effectively to the salvation of souls.
See our earlier article “Eternal Security” for our response to this view.
 Ludwig Ott, Fundamentals of Catholic Dogma (Rockford, Ill.: TAN Books and Publishers, 1974), p.262. White, James R. The Roman Catholic Controversy. Minneapolis, MN: Bethany House, 1996. 43.