Our Father has an eternal plan for his children.  An overall picture of that plan will help us to better understand.  (1) God created this world with his own purpose in mind (Eph. 1:5-11). It belongs to him and he is fulfilling his own purpose for making man.  (2) he has revealed his complete purpose to man in the scriptures.  (3) the great commission gives an overview of this purpose.  (4) He shows us a pathway that will fulfill his purpose.  (5) he shows us the entrance to the pathway.  (6) he reveals the specific steps of the pathway that lead to the goal, his ultimate purpose for man (1 Pet. 2:21). God has a right to make the rules for man to live by because He is the creator and thus total owner and says: “the world is mine, and the fulness thereof of the world and everything in it”  (Psa. 50:12). Contrary to popular thought, he did not create this world simply so that man could enjoy it.  Man’s plans are temporary, but God has a marvelous eternal plan for his creation.

Addendum:

God has never said that the gospel is simple.  The closest we can come to a ‘simple’ gospel is in 2 Corinthians 11:3.  The word ‘simplicity’ is literally singleness (not folded), which is ‘sincerity.’  There are first principles in the gospel for babies (Heb. 5:11-14) but there are second principles of the gospel which are not easy to be understood (2 Pet. 3:15,16).  God hid this wisdom of the gospel from the foundation of the world so that no prophet or anyone else ever imagined what it is (2 Cor. 2:6-11).  He tells plainly that he revealed these things in wisdom.  God’s wisdom is not simple.  Paul preached the gospel in all wisdom (Col. 2:28).  The gospel makes disciples (Matt. 28:19), baptizes those who have been made disciples, and then teaches them all Jesus taught them – the complete truth (John 16:13).  This is not simple.