The explanation for the true church is always and ever the grace of God. Christians are like that. They too dwell in the darkness of sin. Only in time does their election become manifest in effectual calling. Gospel light enters their hearts and changes their lives.
True believers become more and more separated from the world in their conduct.
Their knowledge and holiness are very imperfect in this life, as they will tell you, because sin abounds in them still. So the picture that is given is of dawn, not of noon-day. The church collectively looks forth as the morning in terms of her history in this world. The church makes gradual progress in her knowledge and her understanding of the truth as her Lord is pleased to furnish her with more and more revelation and then more and more light upon that revelation. She makes advance too numerically and geographically.