I think a lot of people have left the church because they have either felt useless or abused. We have corrupted the image of the Body as a group of interlinked, codependent parts, and instead have exalted some parts above others. This is my humble plea as a member of an aching Body in America.
Many people spend years consuming sermon after sermon and song after song without ever knowing the satisfaction of working for the Lord, walking in the good works He has prepared in advance for them to do (Ephesians 2:10). Sometimes this is out of laziness, but I think more often it's because they don't feel needed or equipped. Even though "His divine power has given us everything we need for life and godliness" (2 Peter 1:3), we sometimes believe the lie that we are simply dangling limbs being carried by the preacher rather than active, moving parts of a dynamic Body. We sometimes feel that a seminary degree is a prerequisite for service, even though such a requirement is never found in Scripture. In fact, Paul, even though he proves at the Areopagus that he is certainly knowledgeable about Greek culture and philosophy, deliberately tries to suppress all knowledge not related to the Gospel when preaching because he has "resolved to know nothing while he was with [them] except Jesus Christ and him crucified" (1 Corinthians 2:2). Wow. So just know that simple fact and you're ready to do some pretty amazing stuff.
The fact is, no single part of the Body is expendable. You are not expendable, and we are depending on you to fulfill the mission Christ has for you specifically. All have infinite value and God promises to use every branch that is connected to the vine of Christ to bear fruit - in other words, to heal souls in the same ways Christ did while He was here (John 15:5). What an incredible mission, and what an terrible tragedy that people connected to Christ forget they have this power! So many have turned away because it's so easy for us to doubt our worth simply because a few other people (who have but a breath in their lungs and wither like the grass, according to God!) make us feel small. Don't believe the lie any longer that you're just a money-spewing consumer at church, because you are in fact a vital part of the mission of expanding the Kingdom of God on earth.
Those who have not necessarily felt expendable have been abused. Abuse can come in many forms - gossip, taking others for granted, or prejudice, to name a few. Some have been taken advantage of because of their willingness to volunteer for the jobs no one else will do. Some have been the victims of people who care more about what they can offer (ex. money and time) than about who they are as beloved children. Others have attended "prayer meetings" only to find that they were really gossip groups, or been looked down upon because of teen pregnancy or family problems. Whatever the cause, many have been wounded. And so many attempt to continue their relationship with God without the Church.
The problem is, we can't live in obedience to God if we do not meet with believers regularly, nor can we be filled up with all the blessings He promises us. Not only does He command that we "not give up meeting together" (Hebrews 10:25), but He has formed us to need each other. You not only need us, but we need you! Solomon, the wisest man in the Old Testament, knew this well as he wrote in Ecclesiastes, "Two are better than one, because they have a good return for their work; if one falls down, his friend can help him up. But pity the man who falls and has no one to help him up!" Not to mention that we are told God will be in our very midst if we have two or more gathered in His name. Jesus was hurt by many, many people, even his closest friends, and yet He didn't use that as an excuse to wall himself in on all sides.
This doesn't mean that you should fling your burdens on people who can't bear them. Deliberately look for people who are truly following God, who love Him as you do. I promise they do exist. Dare to dream of a group in which each member "considers others better than himself...not looking to [his] own interests, but also to the interests of others" (Philippians 2). I promise you're not the only person who desires this. In fact, talk to just about any Christian, and she longs for a deeper, intimate community of believers that is upheld by trust and purity. We all want this. We all want to be surrounded by "a great cloud of witnesses" so that we can "throw off everything that hinders and the sin that so easily entangles" (Hebrews 12:1). Forgive those who have hurt you, as Christ has commanded, and dare to allow yourself to be loved again.
We need you back. Unfortunately, churches (because they're made of people, and groups of people in general tend to do this) sometimes act like clubs that require a rite of passage. Take all those reproaches you've heard in the past for not going to church and throw them away. I know this sounds funny because I myself am encouraging you to go to church, but what I mean is that often we invite people to church with an attitude that it's "their obligation" or "their duty," and we take it as an opportunity to demonstrate what good Christians we are by inviting them. BUT our attitude really needs to be one of need, not giving a guilt trip! We NEED you back in the Body. We need more people to encourage us and who will run the race for God with us. God has appointed you to minister to people. There are so many hurting souls who have yet to hear the good news, so many hungry waiting to be fed both physically and spiritually, so many young people who need you to disciple them, so many older people who need you to inject fresh, youthful passion for the Lord into their hearts. So many who would LOVE to have you in their lives and share your struggles and triumphs.
"Now the body is not made up of one part but of many. If the foot should say, 'Because I am not a hand, I do not belong to the body,' it would not for that reason cease to be part of the body...The eye cannot say to the hand, 'I don't need you!' And the head cannot say to the feet, 'I don't need you!'...But God has combined the members of the body and has given greater honor to those that lacked it, so that there should be no division in the body, but that its parts should have equal concern for each other." - 1 Corinthians 12
