This psalm begins with joy and ends with hope, and in between gives us numerous reasons for praising God and trusting in Him. He created the universe and everything that lives. He continues to rule over the earth, and He rules in righteousness and justice. Without God, all the supposed wisdom and strength of nations comes to nothing. With God, there is hope no matter how dire the present situation.
Jesus is giving commands to his disciples, but he is giving them as to friends, not servants. He gives commands so that they will live the way he has taught them and that he has modeled for them, a life of love and joy.