The church was born at the time of uncertainties, tension mixed with confusion. The Jerusalem church was not perfect but maintained unity and a level of purity. That church was a church that prayed and even affected the political terrain of their day. But within a space of 60-65 years, the church began to decay and backslide and the Lord began to call out small groups of people from the churches and these are the ones that are called the overcomers.
Revelation 3:5
He that overcometh, the same shall be clothed in white raiment; and I will not blot out his name out of the book of life, but I will confess his name before my Father, and before his angels.
The children of Israel in the wilderness were also a type of the church while the tribe of Levi were called out as the overcomes. In every age and dispensation there are God's overcomers. God made it possible so that the overcomers would be rapturable. After the rapture the Lord Jesus will return to take the believers who passed through the great tribulation.
The overcomers are men and women who have no sin holding them bound and they also do not love their lives unto death. We are to live the overcoming life and part of what requires us in doing so is by not being bound by besetting sins.