According to the Bible, when God created everything there was no evil anywhere. Everything that God created was God and upright including humans. But something went wrong along the way that brought suffering to mankind.
God created man in His image and likeness, that's means man was created in perfection. There was no evil of any kind, no sickness, and no death. But a twist came into the picture when the first man and woman, Adam and Eve breaks the commandment God gave to them.
This is not something that many of us do not know, but how it relates to the suffering of this world is what most don't understand. In the book of Genesis chapter 2:16, God instructed Adam to eat the fruits of every tree in the garden, but the of the tree of knowledge of good and evil he should not eat, the day he tried to eat of it he shall surely die.
That were simple and clear instructions, yet they failed to obey God. That was the beginning of evil in this world. God said, "the day you will eat thereof, thou shall surely die" and they eat, hence death became the destiny of mankind.
The Apostle Paul explains it better in the book of Romans Romans 5:12 (KJV) where it says "Wherefore, as by one man sin entered into the world, and death by sin; and so death passed upon all men, for that all have sinned:"
The reason for the suffering of humanity originates from the fall of man in the garden of Aden. From that single disobedience of Adam death was passed to all men. We became Sinners by inheritance of the Adamic nature. All humanity shared the sin of Adam, hence all have to bear the consequences of it.
The question now is this, why would God let us suffer if He is a good God that loves and show Mercy?
God allows suffering because He is a God of justice. Whatever God says cannot change. He has said the day man eats that fruit from that tree he shall surely die. So justice must be served. God created everything and gave them boundaries. Nothing can exceed its boundary, the sun, moon, and other planetary bodies moves within their boundaries. Man breaks the boundary God gave, and hence has to face the consequences of death and suffering.
Everything God does is perfect. You can imagine the position of the sun to the Earth. The sun will have to keep to its boundary for mankind to keep living on Earth. Should the Earth be a little closer to the Sun we will all be roasted by the heat coming from it. Should the Earth be a little farther away from the Sun, then we will have to deal with cold that can freeze. We are exactly in the place where life will be sustained on this planet.
That's God's arrangement, and the same thing goes for every area of life. God has set laws to guide both humanity and even natural elements
We must obey God's law and keep to the boundaries God has set for us. If we go against God's arrangements we have to suffer the consequences.
Suffering comes when we break boundaries. That's injustice in the sight of God. Disobedience is the cause of all human suffering. If we do injustice in the family we will suffer the consequences of disobedience. Every evil has its consequences, and because humanity keeps getting eviler suffering keeps getting worse.
We cannot pollute the air by excessive discharge of carbon and expect not to suffer respiratory diseases. We cannot abuse drugs and expect not to suffer the consequences.
God is not to blame for the suffering we are experiencing, instead we have ourselves to blame. We are suffering the consequences of our abuse of God's order. We are the ones who destroyed the Earth by our actions of overdoing.
God made everything beautiful in the beginning, but for Sins everything became course, and as humans continue in the path of sin suffering keeps following. God has no hand in the suffering of humanity, we are suffering the consequences of our actions of disobedience to the commandments of God.