The Bible primarily teaches what man must believe about God and what God requires of man.
I have been offering a few thoughts for each of the questions of the Westminster Shorter Catechism. I have been referencing a modern English version.
God chose to reveal himself through the Bible. Through his word he reveals himself to fallen humanity. The mere words of scripture lack in nothing, but in the capacity to encapsulate all that God is. Man's limited intellect cannot fathom the totality of God's character. God condescends to man, and reveals his character in a manner and substance man is capable of handling. When corruptible puts on incorruptible and we are able to see and feel all that God is, then we will find that our thinking of him now is completely inadequate.
In scripture, God reveals his character and our own character wilts in comparison. God's character can not be condensed to simple platitudes. The complexion of his character and his nature is weaved from the beginning of scripture to the end. There is no contradiction between the powerful vengeful God of the Old Testament, and the ever-loving God of the New Testament. The primary difference between the two is man's thinking about God. God desires men to think rightly of him. He punishes the proud and has mercy on the humble, Those who are capable of recognizing their weakness before a Holy God
God requires men to love. Men are commanded to love because he is worthy of adoration and not because of any benefit that may arise from it. Men are commanded to love one another. This love for fellow-man is required to honor the very image of God that is present in each and every man. We love and serve God by loving and serving our fellow-men who have been created in the image of God.