What Is Revealed?
To answer the question of why there is revelation at all, it is important to know what is being revealed. Revelation is basically the unveiling or the disclosure of truth. Human beings have a rational intellect and a free will, which separates us from the animals and other living creatures on earth. The intellect (or mind) seeks to know the truth. Rather than a subjective judgment or opinion, truth is a correspondence between what one thinks and what actually exists.
Kinds of Truth
There are three basic kinds of truth that are knowable to the human intellect (mind). They are scientific (empirical) truth, philosophical (logical) truth, and theological (religious) truth. Scientific truth is known by using the senses and observing reality. Philosophical truth is known by thinking and using reason. Theological truth is known by faith and believing what God reveals.
Purpose of Revelation
Some things or facts are immediately or easily known by everyone (or are at least knowable to anyone who possesses the use of reason). Some things take more time and effort to figure out, and a few things are so complicated that only a few very intelligent people can know and understand them. Anyone who has reached the age of reason (about seven years old) is presumed to know the difference between lying and telling the truth. A more mature mind is needed to know that ethically speaking, one is not morally obligated to tell everyone everything and yet there is a way to withhold the truth under certain circumstances without telling a lie.
An example of a scientific truth is that fire is hot, which anyone can know by sticking his hand in a flame. A philosophical truth is that nothing can contradict itself; in other words, something can be either real or imaginary, alive or dead, true or false, but it can't be both since either one excludes the other. A theological truth is that the Bible is the inspired written Word of God.
Equality of Revelation
Believers claim that revelation merely evens the playing field since there are some truths (theological) that human beings could never know–either scientifically or philosophically–if God did not reveal them himself. There are other truths that are possible for human beings to know, but–due to differences in levels of education, temperament, environment, culture, etc.–not everyone knows these truths at the same time and in the same way. By revealing both what could not be known by human reason alone and that which is not universally and simultaneously known puts everyone on the same page.
Divine Revelation does not depend on your IQ for you to know and accept it. Faith is all that is needed. Anyone can accept that God exists by believing the revealed Word of God, which says that very thing.