"...the best assemblies are not free from evil ones...This should make us continue to meet with the saints even though we know of some in the assembly who are false to their profession. Should the Sons of God cease to meet because Satan may come among them?...This should make us watchful even while we are praying. This should make ministers faithful, so that the devil may not be at home in the congregation, but may be annoyed by the truth he hates." (Source: Spurgeon's Sermon Notes)
Note: The Devil really hates this sermon: When Government Tries to be God, by Dr. David P. Murray
Recommended reading:
The Conversion of Charles Spurgeon
The Forgotten Spurgeon, by Iain Murray
A Defense of Calvinism - by Charles Spurgeon
The Forgotten Spurgeon, by Iain Murray
A Defense of Calvinism - by Charles Spurgeon