The reason is, as a Christian, you have an enemy in Satan who is as devoted to your destruction as God is to your salvation.
"Be alert and of sober mind. Your enemy the devil prowls around like a roaring lion looking for someone to devour," 1 Peter 5:8.
"For our struggle is not against flesh and blood, but against the rulers, against the authorities, against the powers of this dark world and against the spiritual forces of evil in the heavenly realms," Ephesians 6:12.
To ruin you, the enemy makes sin as easy as possible, and throws stumbling blocks on the path of holiness. As much as you might desire to follow Christ, your enemy is mightier than you.
But not mightier than God.
"You, dear children, are from God and have overcome them, because the one who is in you is greater than the one who is in the world," 1 John 4:4.
The early American Indians had a unique practice of training young braves. On the night of a boy's thirteenth birthday, after learning hunting, scouting, and fishing skills, he was put to one final test. The boy would be placed in a dense forest to spend the entire night alone. Until then, he had never been away from the security of the family and the tribe. But on this night, he was blindfolded and taken several miles away. When he took off the blindfold, he was in the middle of a thick woods and he was terrified! Every time a twig snapped he visualized a wild animal ready to pounce. After what seemed like an eternity, dawn broke and the first rays of sunlight pierced the interior of the forest. Looking around, the boy saw flowers, trees, and an outline of a path. Then, to his utter astonishment, he beheld the figure of a man standing just a few feet away, armed with a bow and arrow.
It was his father.
He had been there all night long.
As dangerous as this world may be, you have a heavenly Father who loves and cares about you, and is ever present to protect you.
"God is our refuge and strength, an ever-present help in trouble," Psalm 46:1.
There might be someone out to get you, but there is Someone greater out to save you.
"Submit yourselves, then, to God. Resist the devil, and he will flee from you," James 4:7.