The Clearness, or “Perspicuity,” of Sacred Scripture
God intended for His Church to guide individuals in their study of the Bible.
Sola Scriptura is the Protestant view (their “rule of faith”) that only the Bible is an infallible authority. Perspicuity is a key aspect or presupposition of sola Scriptura. It holds that the Bible is sufficiently clear in matters of salvation, at least, for anyone to understand without the necessary guidance of any authoritative Christian body.
Is this true? Few things could be conceived as more fatal to the position than multiple hundreds of competing, feuding denominations, where – sadly – much error must be present, according to the laws of contradiction.
Protestant sects started proliferating wildly, as soon as Martin Luther (the founder of the system) set the wheels in motion. He himself despised this tendency, yet apparently failed to comprehend the organic causal relationship between his sola Scriptura and perspicuity and the fruit that they very quickly produced.
The Bible is not perspicuous enough to efficiently eliminate Protestant internal differences. Protestants respond to this objection by maintaining that sin blinds those in opposing camps from seeing obvious truths, which even a “plowboy” (Luther's famous phrase) ought to be able to grasp.
Obviously, Martin Luther himself expected perspicuity to create doctrinal unity, because he was very distraught at the scandalous, ever-increasing sectarianism. People (so he thought) would be free to discover all this “new” biblical truth (from a Catholic perspective, either not new or not true), just as Luther had. Alas, it wasn't nearly so simple.
Yes, sin is clearly a factor in any human affairs, yet to say it is the main reason for hundreds of denominations (rather than a flaw in principle in whole or in part) is a bit much to take.
The problem isn't that “the other guy is blinded by sin....”, it is that we all are blinded by original sin and are thus incapable of establishing a real unity without a central organizing impetus in the Church.
Protestants divide into five major camps concerning the central rite of initiation into the Christian faith:
1) Infant baptismal regeneration (e.g., Lutherans).
2) Adult baptismal regeneration (e.g., Churches of Christ).
3) Symbolic-only infant baptism (e.g., Presbyterians).
4) Symbolic-only adult baptism (e.g., Baptists).
5) No baptism required at all (e.g., Quakers, Salvation Army).
Since this debate hasn't been able to be resolved, many simply deny that baptism is “central.” Yet the Bible insists on the crucial nature of baptism:
Mark 16:16 He who believes and is baptized will be saved; . . .
Titus 3:5 he saved us, . . . by the washing of regeneration and renewal in the Holy Spirit, (cf. Jn 3:5)
1 Peter 3:21 Baptism, which corresponds to this [Noah's ark], now saves you, . . .
The Apostle Paul referred to “one Lord, one faith, one baptism” (Eph 4:5). The Catholic, when studying the Bible, wants to know if his interpretations are in line with those of the Church, and apostolic tradition. In this way, doctrinal unity can be maintained.
It's not that Scripture is so unclear and esoteric that it is an utter mystery and an undecipherable “code” that only Holy Mother Church can break, and that no individual can possibly understand. Rather, the Church is required to speak authoritatively as to what Holy Scripture teaches, just as it spoke authoritatively with regard to what books were to be included in Scripture. Holy Scripture remains inherently what it is: God's inspired, infallible written revelation.
Tradition in the Bible (particularly for St. Paul) is not an individualistic thing, kept by each person as an esoteric “secret,” as the gnostic heretics would have it. No, it is obviously a corporately held entity. It is held in common by the Church, as the collectivity of Christians. And as this deposit of faith was one unified teaching, there necessarily had to be one Church to preserve and promulgate it.
Baptism and the Eucharist are indeed “primary” and “essential” doctrines – precisely the sort of beliefs that a perspicuous Scripture is supposed to resolve. Yet they have not been resolved; ergo: this understanding of perspicuity is false. Our Lord Jesus directly connects the Eucharist and salvation:
John 6:50-58 “This is the bread which comes down from heaven, that a man may eat of it and not die.  I am the living bread which came down from heaven; if any one eats of this bread, he will live for ever; and the bread which I shall give for the life of the world is my flesh.”  The Jews then disputed among themselves, saying, “How can this man give us his flesh to eat?”  So Jesus said to them, “Truly, truly, I say to you, unless you eat the flesh of the Son of man and drink his blood, you have no life in you;  he who eats my flesh and drinks my blood has eternal life, and I will raise him up at the last day.  For my flesh is food indeed, and my blood is drink indeed.  He who eats my flesh and drinks my blood abides in me, and I in him.  As the living Father sent me, and I live because of the Father, so he who eats me will live because of me.  This is the bread which came down from heaven, not such as the fathers ate and died; he who eats this bread will live for ever.”
How, then, can there be multiple interpretations of the Eucharist (as also occur in Protestantism)? It's a central doctrine, essential to salvation! Multiple parties are all approaching Scripture with open-mindedness and willingness to follow it, yet they still disagree. We may freely affirm that Calvin and Luther were both utterly sincere in their commitment to Holy Scripture as authoritative. Yet they couldn't agree on many fundamental issues (including baptism and the Eucharist: Luther being much more traditional and “Catholic”).
Therefore, it is reasonable to conclude that perspicuity is untrue. God intended for His Church to guide individuals in their study of the Bible (Acts 8:27-31).