If I were to teach someone about who God is, then I would start by speaking about what He has commanded. For example, seeing that God has given wise, holy, righteous, and good laws, they can see that God is wise, holy, righteous, and good, and so forth for other aspects of God's nature. If God were to have commanded His people to commit adultery, then that would have taught us something very different about the nature of who He is, so all of God's commands paint us a picture of He is. Likewise, I would teach someone about who God is by testifying about the things that He has done. Keeping the Sabbath holy testifies that there is a Creator of the world who created it in six days, who rested on the seventh, who is holy, who sanctifies us, and who saves His people out of bondage, so if we believe that these things accurately describe the God that we believe in, then we will live in a way that testifies about their truth by keeping the Sabbath holy.