WHAT IS A MYSTERY?
It is anything that is kept secret or remains unexplained or unknown: the mysteries of nature. we have The mystery of the bible.
Dear brethren have you ever been in a situation where you as a Christian passes through trials and temptations? At times God choses to bless whoever he wills, that alone is a mystery. When you turn around you see your enemies prospering and you struggling to survive never give up and say there is no God.
Things like that is allowed by God to most importantly taste the faith of man, but you should also know that no matter how rich and successful your enemy may be God is never happy with the wicked, that was the reason he made hell for the wicked ones and their master the devil.
But note that if you are in Christ surely you are rich, because remember silver and gold is of the lord. They was a question Habakuk asked the lord he said why will the wicked always enjoy in riches? But it should not be the reason we go astray, because they is hope for the righteous man.
Prosperity of the wicked is what we see as a mystery, and can be explained by God alone.