There are two descriptive terms in the Bible, which illustrate the power of the presence of the church in a dark, sinful world -- light and salt.
Jesus told His disciples, and in turn, the New Testament church in Matthew 5:13, "Ye are the salt of the earth..."
Also, Jesus told them in Matthew 5:14, "Ye are the light of the world..."
Light dispels darkness. It is impossible to have a completely dark room as long as there is at least a tiny flicker from a match or a candle. In a dark world, such as we live in today, the presence of the church casts light on it. Let me explain. In the workplace, there may be all sorts of vile language spew out of men's (and women's) mouths.
But let a genuine believer in Christ walk up, and often the crowd will dissipate. Someone may allowed a word to slip in the presence of a Christian, and tension may fill the room. This should be the normal effect members of the Body of Christ have on the world every day.
How does salt illustrate the presence of the church? Salt gives flavor; it is a great healer; it is a preservative; it is a purifier; and when it is applied to an open wound, it stings. These are effects the New Testament church has on society.
The church possesses these traits because (1) Christ is the Foundation of the church (Matthew 16:19) Jesus told Peter that upon "this rock" (which was not Peter, because Peter is petros — a tiny pebble). Then Jesus said, "but upon this rock (petra -the foundational stone, which is Christ,) I will build my church and the gates of hell shall not prevail against it." (2) The church was empowered with the Holy Spirit, some 50 days after Christ ascended back to the Father. (Acts 2) Being a spirit-filled, spirit-led entity on this earth, the church has power and authority not given to any other entity or organization.
When people become followers of Christ and join themselves to the New Testament church, they have become enjoined to the manifestation of the presence of God the Father on this earth. Never, never take the church flippantly, and, as scripture says in Hebrews 10:25, "Not forsaking the assembling of ourselves together..."