"The New Testament, written in Greek, used the word ekklesia to describe 'C/church.' Ekklesia is a compound word consisting of ek, meaning 'out of,' and klesis, 'a calling.' Used one hundred and fourteen times, ekklesia is sometimes translated as 'assembly' (three times), 'church' (seventy-four times), 'churches' (thirty-five times), and 'congregation' (two times.) Therefore, whatever the C/church is, it consists of a group of people who have recieved a calling out of something for a particular purpose." - J. D. Payne, Missional House Churches, p. 21-22.In answering the question as to why Christians need a local church, it is important to consider the original word that is translated as church. As the early church was forming they needed a word to use to talk about this new thing, the church. They landed on the word that was currently used for an assembly. Whenever there was need for a meeting of the people in the town a herald would go out and summon people to come together in a certain place to meet and discuss the issue at hand. The word ekklesia was used to refer to those people who had been called out.
How does this word paint the picture for the church? Let's consider what Jesus said in John 5:24-25:
"Truly, truly, I say to you, whoever hears my word and believes him who sent me has eternal life. He does not come into judgment, but has passed from death to life. Truly, truly, I say to you, an hour is coming, and is now here, when the dead will hear the voice of the Son of God, and those who hear will live."Let's put this together with what Paul explains to the christians in Ephesus about what happened when they were saved.
"But God, being rich in mercy, because of the great love with which he loved us, even when we were dead in our trespasses, made us alive together with Christ." Eph 2:4-5So let me ask you, have you heard the voice of the Son of God? Has he thus made you alive and called you out of your death and darkness? The church is the gathering or assembly of those who have been called to follow Jesus. From the origin of the church it's name symbolizes the fact that it is made up of a group who has been called out. The Holy Spirit is the herald who calls us out of darkness into the light, and anyone who has been called out is expected to come together. So, from the beginning of Christianity, the idea of a Christian who does not assemble with other Christians is a foreign concept.
I leave you with this instruction from the Apostle Paul to Titus:
"For the grace of God has appeared, bringing salvation for all people, training us to renounce ungodliness and worldly passions, and to live self-controlled, upright, and godly lives in the present age, waiting for our blessed hope, the appearing of the glory of our great God and Savior Jesus Christ, who gave himself for us to redeem us from all lawlessness and to purify for himself a people for his own possession who are zealous for good works. Declare these things; exhort and rebuke with all authority. Let no one disregard you." Titus 2:11-15