Deuteronomy 4   Moses reminds the people of Israel of the reason they are to keep the Laws of God.

That reason is "so that you may live".   Don't add to it, don't take anything away from it, Moses teaches.. but, "behave accordingly".   They were to observe and follow the Law so that "all peoples will see you as having wisdom and understanding."   A nation that lived according to God's Word would be a great nation.. a respected nation.  They would be a Light to other nations and a testimony to the greatness of God.

Israel was God's chosen inheritance .  He is " a consuming fire, a jealous God".  He would not abandon Israel and He desired for them to keep the covenant they had with Him.  And even when they would go astray, He would be merciful to them and never fail them, destroy them, or forget the covenant He made with Abraham.  Never before in the history of the world, Moses taught, did God do anything like He did with Israel:

Israel heard God's voice "speaking out of the fire" from the mountain.
Israel was rescued out of Egypt with "ordeals, signs, wonders, war, a mighty hand, an outstretched arm and great terrors..." 
" This was shown to you, so that you would know that Adonai is God, and there is no other beside him." (v35)

The reason Israel needed to obey God's law was so that they could live forever with Him.  ".. know today, and establish it in your heart, that Adonai is God in heaven above and on earth below- there is no other." 

Like Israel, the church has be called to live according to God's Word, to be seen as having wisdom and understanding, to testify that He is God and there is no other!  Our God speaks to us, not from the fire on a mountain, but through His Spirit and His Word.  He has rescued us from the dominion of darkness and brought us miraculously into the Kingdom of His beloved Son.  He has shown us that He alone is God and there is no other!   Adonai made a covenant with Israel and He has made a New Covenant with all who will trust in Jesus Christ as Lord. He has written His laws on our hearts and given us His Spirit that we might live in fellowship with Him.

Father , even now we ask that You would help us to live accordingly.. fully surrendered and obedient to You, our Great and mighty God.  There is none like You!  Empower us, Your Church, to be all that You have called us to be.  To God be the glory. Amen.