This is a part of the Calvin's Institutes summary series post #2.
To know God as the Creator is to know that absolutely everything is made by Him and all good things (such as wisdom, light, righteousness, power, rectitude, truth, etc) come from Him. Hence, knowing God requires one to be pious, ie. to revere and love God.
Theoretical-only knowledge of God is a useless speculation as is irrelevant. True knowledge of God is a practical knowledge. We ought to know what God is like and respond rightly. To do so, we must not imagine what God is like, but rather, carefully pay attention to His own revelation.
"Here indeed is pure and real religion: faith so joined with an earnest fear of God that this fear also embraces willing reverence, and carries with it such legitimate worship as is prescribed in the law."