Summary: There is a belief within the church that the Creator God has a perfect will with as many as six permissive variations
There is a belief within the church that the Creator God has a perfect will with many permissive variations that purposely 'allows' horrible things such as sickness and disease to happen to those who He created in His image and likeness (James 3:9).
"And be not conformed to this world: but be ye transformed by the renewing of your mind, that ye may prove what is that good, and acceptable, and perfect, will of God." (Rom 12:2 KJV)
The word “and” is an English syntax from the Greek conjunctive 'kai,' which connects single words, terms, sentences, whole narratives, and expositions. The verse does not mean that God has different wills - a good will, an acceptable will, and a perfect will. Instead, it says that the only will (singular) of God is good, acceptable, and perfect.
The Bible does not speak of multiple 'wills' of God. There is only one will - which is His perfect will. God does not 'permissively' allow tragedy, murder, rape, racism, child abuse, sickness, disease, etc. If a person gives permission to (i.e., allows) someone to use their car and knows that person will get drunk and kill someone, they are as responsible as the person who got drunk. To say that God ‘allows’ horrible things is the same as saying He is responsible and is blaming Him indirectly for it - which He is not. There is simply no Scriptural support for this supposition. If you or I were accused of treating our kids the way God is accused of treating His, we would be arrested and locked up for child abuse - and they would throw away the key!!
The English word "allow" is defined as "to forbear or neglect to restrain or prevent." God does not condone, permit, allow, give, punish, or approve of any sickness, pain, disease, etc. He wants only the best for His people, who He calls His Bride, because He is head over heels in love with her. Sickness and disease, etc., are not "best" things. It is one of a legion of effects brought about by the Fall of Adam and Eve. The disease of death will never be healed in this life. God desires to pour out (not restrain!) blessing upon blessing to those who trust Him with their entire being (Rev 21:9).
Ultimately, it doesn't matter who is to blame for sickness or disease, etc. What is most important is that God is looking for those who will trust Him no matter what. The Bible tells us how to live a long and healthy life, but it does not promise a sickness or disease-free life because we all will die from them one day. Blame it on Adam and not God.
The Bible declares that "in all things God works for the good of those who love him, who have been called according to his purpose" (Rom 8:28 NIV). Note that it does not say that God "causes" or "allows" bad things to happen so that He can test or try one's faith to make them a "better" or "stronger" person or to discipline or punish them.
God's great promise is that He will enter INTO every circumstance to make it right and work it out for the best. God doesn't create horrible circumstances so that He can provide "opportunities" to prove He is faithful or so that people can prove they trust Him during hard or trying times or grow spiritually! Nor does He use or allow them as "loving" correction of His children.
God will never neglect His Bride or prevent her from experiencing deep intimacy when she cries out in desperate longing for more of Him. He has blessed her with every spiritual blessing (Eph 1:3). He only gives her gifts that are good and perfect (James 1:17). Pain, tragedy, sickness, and disease are diametrically opposed to good and perfect.
God has only one Will - His perfect sovereign Will. He is omniscient and knows all truth in every potential situation, whether before the beginning, in the middle, or at the ending under all possible interpretations of any component. God knows everything that does, will, or could happen. Before God spoke the world into existence, He knew independently what every person would freely choose if placed in any possible circumstance.
God alone grants salvation. Because He is love, He gave human beings the free will to accept or reject Him, love or hate Him. He knows what choices a person will make, whether they are good or bad, just as a parent can understand their child's choices in a given situation, whether or not they actually make them. He perfectly accomplishes His will in their lives (Matt 11:23). He knew that sin would enter into the world, but He is not the author of sin. God does not actively bring about overt acts of sin because He is a good God, and it is His goodness that leads a person to repentance (Matt 19:17; Rom 2:4).