All Catholic beliefs can be found in the Bible in some form, whether plainly or by an indirect indication. It is not necessary for everything to be absolutely clear in Scripture alone, because that is not a teaching of Scripture itself. Scripture also points to an authoritative Church and Tradition, as St. Paul says in his Second Letter to the Thessalonians: "Stand firm and hold to the traditions which you were taught by us, either by word of mouth or by letter" (2 Thess 2:15 - see also 1 Cor 11:2, 2 Thess 3:6; 2 Tim (1:13-14; 2:2).

When the first Christians had a significant disagreement, they didn't simply open their Bibles (which didn't even exist at that point) to decide who was right; they held a council, which made binding decrees (Acts 15:1-29). The very books of the Bible had to be determined by the Church and that didn't happen until the late fourth century. Therefore, Sacred Tradition and authority were necessary for us to even have a Bible today.