Why would God sanctify His day of rest (cessation from creating)? Four observations point us toward the answer.
First, His rest is the perfect conclusion to His work of creation. After God completed His creation work (Genesis 1), we don't find Him scrambling around the universe to fix poor designs, to educate Himself on parts of the universe beyond His knowledge, or to quell opposition to His reign. Instead, He rests--perfectly in control of all He has done, knowing everything about all He has created, and ruling absolutely in supreme freedom. What a fitting celebration of His character!
Second, His rest is ongoing. "The works were finished from the foundation of the world" (Hebrews 4:3). Since creation, God has never second-guessed His activity, tried to create the universe again, or given any hint that His initial creation was somehow flawed. It was exactly how He designed and planned it from the start. Who else could create so perfectly and completely?
Third, His rest is holy. No man has ever created like God did, and, therefore, no man ever rested like God did. While man enjoyed a measure of rest (from toil) in the beginning, he lost it when he sinned (Genesis 3:17-19), and he has been laboring against opposition to his rule ever since then. God's rest is utterly unique.
Fourth, His rest is wonderful. God can withhold rest from His fallen and depraved creatures. Yet He offers rest to those who believe through Christ! "Come unto me, all ye that labour and are heavy laden, and I will give you rest" (Matthew 11:28).
What profound and glorious reasons God had to set apart His day of rest! NTJ