Because I said so
A famous saying parents used to say to their children when their children were questioning why they had to do what their parents were telling them was, "because I said so". This usually came when the parents had grown weary of being questioned and out of frustration issued the phrase that was to end the conversation and demand compliance. Another version was ,"because I'm you're father/mother". The child was supposed to get the message that they had pushed far enough, and continued questioning would be met with another level of response which would be less pleasant.
It is normal for children to ask questions. It is even to be expected that children will occasionally challenge the authority of their parents as long as they do not go too far with it. Parents need to understand that what children are doing is testing their parents to see if they will stand their ground. The children usually do not want their parents to fail. Inside they are actually wanting their parents to be strong because this reassures them that their parents love them, there are boundaries to behavior, and authority has meaning. This gives them a sense of security. Parents who do not discipline their children are undermining their own children's ability to mature. Parents who threaten their children but never follow through lose the respect of their children. It does not take long for kids to learn that their parents' word means nothing. It sets them up for problems with authority in their future. When my children would test me, I would tell them that no one in this world loves them more than their parents. I would tell them that they will always be under someone's authority, so if they cannot learn to properly interact with their parents' authority, they will have serious problems later dealing with people in authority that do not care about them like their parents do.
We all have to relate with authority. We decide how that is going to go. We can obey proper authority and be blessed, or we can fight it and be cursed. For example, we can follow the law and enjoy freedom, or we can break the law and go to jail. The generation that fought World War II is called the greatest generation of Americans. The sacrifices and bravery they showed fighting tyranny is commendable. However, the sixties (especially the last several years) was a decade with the motto "question authority". There is a difference between asking questions in order to understand and being rebellious. The children of the "greatest generation" were the sixties generation. The problem is once it started, it kept going and growing. We are now on the third generation "questioning authority" and the results are not good.
God is the ultimate and final authority. All authority ultimately comes from Him (Rom 13:1-7). That does not mean God condones what everyone in authority does. For a further study on authority issues, you can read "Does Might Make Right?" available on this website. However, the principles that apply to parents and children apply to our relationship with God our Father. We can ask Him questions in the right attitude, but He is not obligated to explain Himself to man. Sometimes God says the reason He is telling us to do something is because He is the Lord. This phrase appears 161 times in the Bible, especially in Leviticus 18-26. We need to have faith in and respect for God, and that He knows what He is doing; because sometimes the answer is ,"because I said so".