This is a question that could surely be answered far better than I can answer it, but one part of the answer to why God says what He says in the Word He’s given, is that His ways are above our ways. He understands human action, the thoughts and intentions of our hearts, and how to avoid sin.
We can say that certain parts of Scripture do not apply to us, but we are deceived if we honestly think that. God is God, and He understands the consequences to going our own way.
For example, the way children are disciplined plays in mightily to their attitude. It is not hard to cause children to develop sulking, brooding, or angry attitudes. I recall being sent to my room as a youngster and how I would think vengeful thoughts. It took me time to get over my anger problem and negative way of thinking when I felt wronged. I was not disciplined biblically (the Bible is clear on swift discipline that brings physical discomfort) and the training did not succeed in addressing and redirecting my thinking. It was action oriented, which only did part of the job. God understands human development far better than we do, and young children respond well to the way God has outlined it. There is no need to yell at your kids or get angry with them (people learn angry ways by being with angry people the Bible says), discipline them as God says and it is effective and over with quickly.
What about not being surety for another’s loan? We can justify when this is OK, using our human logic. But it isn’t always about the person repaying–though of course that is a huge part of it. What of encouraging others to work and save to the point they don’t need someone to be surety? A pattern of buying what cannot be afforded is easily begun when parents co-sign for their kids.This generation knows nothing of the ways our grandparents and their parents before them lived. We want what we think we need, and we borrow to get it. God tells us the servant is a slave to the lender, and the older generations knew that. Look at the size of the homes our grandparents had. None had the spacious homes we all have today. The lifestyle we lead perpetuates the value system we’ve adopted, so we ‘must’ have vehicles to go and do this and that, we must have cable TV, we must have smart phones with fancy data plans etc. Where does God fit in to this? We ignore Him and do what we want, then have the audacity to ask Him to bless and help when we need it. Of course, His ways are not our ways, and He is continues to be gracious toward us.
These are just two examples, but there are loads more. As followers of Christ, we do not obey God because we’ve reasoned out what He says and in our estimation, it is worth listening to. If we are Christians, we do what He says because we trust Him. We come willing to be shown the error of our ways, and we take on His ways. Often, He’ll show us the ‘why’ of it later, but even if He doesn’t, we can rest confident in the fact we’ve followed the One who knows, and who is always trust worthy.
Trust in the Lord with all your heart and lean not on your own understanding, in all your ways acknowledge Him and He shall direct your path. Be not wise in your own eyes, fear the Lord and turn away from evil.