Why is becoming a Christian so simple, yet so difficult?

It's simple because the requirements are extremely simple: Confess Jesus as Lord with your mouth, believe that God raised Him from the dead in your heart (Romans 10:9-10). It's difficult because we humans are naturally disposed to hide from God, and because Satan tries with excellent effect to keep us from God, and God from us. We read that "the god of this age has blinded the minds of those who don't believe;"(2 Cor. 4:4); Jesus says, "[Satan] was a murderer from the beginning..." meaning that he sought to spiritually destroy Adam and Eve with his cunning lies. It's the first thing the devil did with man, and it's the last thing he'll do (see Revelation 20:7-10). Satan's power is hidden, for the most part, especially in the West, and consists of deception, temptation, and outright invasion. Against this, God seeks you out, and calls to you through His Spirit. LISTEN!
It's only because of God that we find Him.  He says, "Seek Me with all your heart, and you'll find me;" but we never seek Him unless He calls to us. Instead, it's in our nature to hide from Him, just as Adam and Eve did, after they ate from the fruit of the tree of the knowledge of good and evil. We read that they "hid from the LORD" when "He was walking in the garden of Eden in the cool of the day." However, this verse (Genesis 3:8) is followed by: "The LORD called to the man, and said to him, 'where are you?'"
So the very first time man hid from God, God sought him out. God is seeking you. He is seeking you now.
If you are far from Him and think you cannot find Him, He's not far away.  As the book of Acts says, "He is not far from every one of us, for it says, 'in Him we live and move and have our being,'"   or as it says elsewhere, "draw near to God, and He will draw near to you;" this speaks of intent, and decision.  You feel far from God? Seek Him. You feel like He's not there, that He's not listening, that He's silent? Call out to Him.  Don't be afraid.  He is right there, right next to you, right next to me, right close to each of us.
If you stop hiding, you'll find Him for sure. And don't forget.  You won't have to go far to find Him, since He's seeking you.

Faith--> God's blessing and approval

Faith: Brings God's approval, Salvation, a life full of blessing:
"Now faith is the assurance of things we hope for, the things we don't see; for by it the elders (those who've gone before) gained approval"
"If you confess Jesus as Lord with your mouth, and believe in your heart that God raised Him from the dead, you shall be saved (from eternal destruction)."
"Whatever things you desire, believe that you received them, and you shall have them..."
Faith has rightly been called the "hand of the heart;" with faith, we reach out to God, and receive the blessings He wants to give to us--as He says, "All the promises of God [Christ] are "YES" in Him..." whatever God has promised comes to you by faith.
Want to know more?  Read Hebrews 11.