JOHN 13:31-35
The characteristic of a Christian, according to Jesus, is our love for one another. Possessing true love for other believers isn't a priority for most Christians. But, Jesus said that it is the #1 thing that will show unbelievers that He is real and alive in us.
The Church, as a body, has put a huge amount of money and effort into reaching the lost. Buildings have been built with cushioned seats, A/C for comfort to attract more people. Crusades are held to reach more people, yet, our love for each other is lacking which He said would represent Him the best.
The first biblical church didn't have the things that it has today. They met in homes and out in the open fields without the comforts we have but made a tremendous impact on the world with the Gospel.
Jude said the early church meetings were "feasts of charity", Jude 1:12. Love abounded then and so did the Gospel.
We must choose to be a living advertisement for the Gospel by allowing God's love to shine through for all to see as well as the lost. Unbelievers will then know that Jesus is alive in us.