You will notice that in question 25 of the Catechism, when asked about the Trinity, the answer begins with the language of “because God revealed…” At first, that might seem like a simple enough phrase and one that is not that important, yet, from the perspective of the Christian faith, it is of significant value. While indeed, the creation testifies to its creator (Psalm 19:1; Romans 1:20), such knowledge is not sufficient to save or to produce saving faith for faith comes by hearing the Word of Christ, not by works or by innate knowledge (Romans 10:17; Galatians 3:2). Further, that Word cannot be found in nature…no matter how hard you may look or how far you may search. That word must be revealed to us by God himself.
With this in mind, we Christians have a faith that is a “revealed faith.” Apart from the revelation from God, we are lost forever. Left to our own devices, we will seek to earn a salvation that we can never earn and thus be lost in despair. Left to our own devices, our imaginations will create gods after our own image which would be molded by our own hands — little gods that cannot save us from our sins. Left to our own devices, we will create philosophies that will justify our own preferences, thus leaving us in utter moral relativism where each man essentially becomes his own god.
And so, God reveals himself to us and while he did so in many ways (think Hebrews 1:1 — dreams, prophesies, history, poetry, wisdom sayings, etc…), the culmination and compilation of the entirety of God’s revelation is found in His Word. Nothing outside of the Bible (66 books, Genesis-Revelation) is the Revelation of God and thus even the most noble and wisest observations of men must be scrutinized by the light of God’s revelation (not the other way around as is done in many liberal circles).
The sad thing is that many people today would prefer subjective experience to the objectively revealed Word of God. Many prefer their own pragmatic insights to the revealed wisdom of God on high. And many more would prefer a god of their own making to the God of Heaven. Many prefer a god they can control rather than a God who can make demands of them. Such is the nature of fallen man and such is what distinguishes Christianity from every other religion — for Christianity is a revealed religion, not one constructed by men.