In the world you will have tribulation.John 16:33
Are you asking why this should be, believer? Look upward to your heavenly Father, and behold Him pure and holy. Do you know that you are one day to be like Him? Will you easily be conformed to His image? Will you not require much refining in the furnace of affliction to purify you? Will it be an easy thing to get rid of your corruptions and make you perfect even as your Father in heaven is perfect?
Next, Christian, turn your eye downward. Do you know what foes you have beneath your feet? You were once a servant of Satan, and no king will willingly lose his subjects. Do you think that Satan will leave you alone? No, he will always be at you, for he "prowls around like a roaring lion, seeking someone to devour."1 Expect trouble, then, Christian, when you look beneath you.
Then look around you. Where are you? You are in enemy country, a stranger and an alien. The world is not your friend. If it is, then you are not God's friend, for whoever is the friend of the world is the enemy of God. Be certain that you will find enemies everywhere. When you sleep, remember that you are resting on the battlefield; when you travel, suspect an ambush in every hedge. As mosquitoes are said to bite strangers more than natives, so the trials of earth will be sharpest to you.
Lastly, look within you, into your own heart, and observe what is there. Sin and self are still within. If you had no devil to tempt you, no enemies to fight you, and no world to ensnare you, you would still find in yourself enough evil to be a sore trial to you, for "the heart is deceitful above all things, and desperately sick."2 Expect trouble then, but do not despair on account of it, for God is with you to help and to strengthen you. He has said, "call upon me in the day of trouble; I will deliver you, and you shall glorify me."3
1) 1 Peter 5:8
2) Jeremiah 17:9
3) Psalm 50:15