The only way God can prove to the entire universe what the consequence of sin is, is by allowing sin to run its course, to avoid sin from ever surfacing again. The pain and suffering that God has had to endure since sin entered heaven is unfathomable – if He had not allowed sin to perpetuate and destroyed the sinners (Satan and his angels) on the spot, His creatures would have obeyed him solely out of fear, and this is not the nature of God. He is love, from the beginning God was love, in other words, before creation, love existed within the Godhead (3 living beings in the Godhead), freely given and freely received.
Now, the same applies in our world – we have a choice to either follow God or to reject Him. God knocks on our door, if we do not open the door for him to enter our life, He cannot force us to love Him or obey him. God is love, He does not coerce whereas Satan has the “upper hand” in this regard, he does coerce, he is a mighty deceiver, and will do everything in his power to separate us from God – whether we follow him or not, that is irrelevant to him. This unfortunately leaves those who reject God vulnerable to the deceptions of Satan – but God has given us ample warning regarding the adversary and the repercussions in His word (from Adam and Eve and everyone till this day). Suffering exists due to sin, and if we constantly reject God and choose Satan’s ways, there is nothing God can do for us – if God were to intervene in this case, the element of “freedom of choice” would no longer apply and Satan would accuse Him of this – the wages of sin would thus be blurred for the entire universe. We will only fully understand the sacrifices God has had to make for mankind one day in heaven – God calls every one of us to Him, and most will reject Him and still blame Him for their sufferings. When Adam fell, Satan claimed the world under his control, and rightfully so – our faith in God was not strong enough and we rejected God for the pleasures that sin has to offer – but God devised a plan that, whosoever believeth in Him, shall not perish but have everlasting life.
A similar question in detail should you wish to take a look – please follow link below.
God will allow suffering for other reasons as well – to build our characters and allow us to learn from our mistakes – this is the tough part of the sanctification process but, in order for us to find our way back to God, the chains of this world will have to be broken from our bodies and we will have to become a new creature in Him.