Faith is concerned with truth not naturally accessible to the mind of man. However it is a fact that God has also revealed some truth that human reason could discover, such as the existence of God, the immortality of the human soul, and the like. God has done this because He knows that many men, through lack of talent or opportunity, or even through mere laziness, might never come to the knowledge of these important thruths. Whenever man cannot discover these truths for themselves, it is possible for them to learn these truth through faith in God's word. But primarily faith is concerned with the mysteries of God in Himself and in His actions in the world which men could never discover for themselves.
Faith is then an enlargement of the horizons of the human mind. It lifts the mind of man above the world of nature and sets it free in the limitless world of the DIvine Being. It introduces man to that great mystery of the Divine Life, the Trinity. It makes man aware of God's stupendous entrance into human life through the Incarnation of the Son of God in Jesus Christ. It informs man of the divine generosity in making the vision of God possible for men. It gives man a knowledge of the supernatural means by which he can attain the vision of God. Faith does not impose limitations on the mind of man. It removes them. Through faith the mind of man is no longer subject to the imperfections of the senses or of human reason. Through faith man is given a share in the infinite perfection of God's own knowledge. If man's ultimate goal is the vision of God, then faith, which gives man some knowledge, even though an obscure knowledge, of God as He is in Himself, is a beginning of happiness in human life. It puts man on the road to ultimate happiness.
God, the object of faith is in Himself absolutely simple. But the simple things are often the hardest to understand or explain. For example, if we look at a lever, it is a simple thing, but how many words, sentences or even paragraphs may be necessary to explain its power to lift great weights. So it is with God. Because He is absolutely simple, the human mind, which understands things bit by bit, cannot grasp the Divine Being simply. It must, as it were, go round God slowly, viewing Him now from this angle and now from another angle. It will express each of these different viewsof the one simple object - God - in a separate judgment or proposition. In revealing Himself to man God has taken account of this weakness of the human mind. He has revealed Himself to man bit by bit, sentence after sentence.
These truth or judments about God, which God has revealed, make up the content of faith. They are many and they were revealed to man over long period of time, from Adam to Christ and His Apostles. Because God is absolutely one and absolutely simple, some of these truths are contained implicitly in others. From the point of view of the human mind which accept these truths in faith, we may reduce all the revealed truths about God to the mysteries of the Trinity - God as He is in Himself - and the Incarnation - God as He enters the world supernaturally to accomplish the salvation of man.
after "My Way of Life - The Summa Simplified"