Why does God let bad things happen to His children?

Christians commonly wonder why our lives on earth includes difficulties, trials, tragedy and sadness even after we have become a follower of Jesus Christ and an adopted child of God. But the Bible never assures believers that life on earth will be trouble-free simply because we have become followers of Jesus. In fact, the Bible tells us exactly the opposite:

John 16:33 “These things I have spoken to you, so that in Me you may have peace. In the world you have tribulation, but take courage; I have overcome the world.”

The believer is promised to experience tribulations while we live on earth, in part because the world is a fallen, sinful place where the enemy has dominion for a time. Moreover, because we are children of God, that enemy will make things difficult for us, leading us to disobey God:

Mark 10:29 Jesus said, “Truly I say to you, there is no one who has left house or brothers or sisters or mother or father or children or farms, for My sake and for the gospel’s sake,
Mark 10:30 but that he will receive a hundred times as much now in the present age, houses and brothers and sisters and mothers and children and farms, along with persecutions; and in the age to come, eternal life.

Notice that Jesus says in v.30 that believers will experience persecutions for having chosen to follow Jesus. The enemy of God is also our enemy, and so we should expect him to bring adversity our way for as long as we live on earth. So believers will experience “bad” things on earth because of the sin of the world around us (including our own sinful choices) and because of the enemy’s effort to discourage our obedience.

Nevertheless, we might ask why doesn’t the Lord protect us from these things? Scripture gives us the answer:

Rom. 5:1 Therefore, having been justified by faith, we have peace with God through our Lord Jesus Christ,
Rom. 5:2 through whom also we have obtained our introduction by faith into this grace in which we stand; and we exult in hope of the glory of God.
Rom. 5:3 And not only this, but we also exult in our tribulations, knowing that tribulation brings about perseverance;
Rom. 5:4 and perseverance, proven character; and proven character, hope;
Rom. 5:5 and hope does not disappoint, because the love of God has been poured out within our hearts through the Holy Spirit who was given to us.

Paul says that in allowing believers to experience tribulations the Lord is working on our behalf to develop spiritual maturity and a godly character. Specifically, by our perseverance we become even more resolved to obey and serve Christ. That godly character inspires a greater hope and anticipation of our eternal future in glory with Christ, and it gives the Lord opportunity to bless us with greater eternal rewards in that day. 

As James says:

James 1:2 Consider it all joy, my brethren, when you encounter various trials,
James 1:3 knowing that the testing of your faith produces endurance.
James 1:4 And let endurance have its perfect result, so that you may be perfect and complete, lacking in nothing.

So when a believer experiences “bad” things in life, he or she should bring a biblical perspective to that moment. The Bible says we should count it joy because it means that the Lord has counted us worthy to receive this spiritual training. And as we endure the trial, we are gaining eternal things that will leave us complete, lacking in nothing.