It occurs to me that many in the body of Christ are just "easy picken's" to the enemy. The average Christian is easily offended and easily distracted. Most are sense dependent taking what they believe not so much from God's word but from what they see, hear, feel, touch and sense from the natural world around them (I Cor. 2:14). Many are easily entangled with judgments, and being judged; remaining under the law (Gal.5:1). Many are busy with worldly things such as sports, programs, family obligations, career, money, and entertainment, etc. that conflict with being committed to the things of God (Matt. 6:33). Many have a dogmatic view of scripture. They are fixed, rigid, and convinced they are right. Often this manifests with people straining at gnats and swallowing camels (making mountains out of mole hills) like the Pharisees of old (Matt. 23:24). These things and more (and there is unfortunately a lot more) lead people to become disgruntled, disinterested, and either leave or stop coming to a church.
Over the past five or so years God has shown me His amazing Grace and true faith...He's broken through the glass barrier of doubt & unbelief, and has made the gospel so much clearer. It's not on us...it's on Jesus! All things are possible to Him who believes--Jesus is the One who believes.