While Apollos was in Corinth,
Paul traveled through the interior of the country
and down to Ephesus where he found some disciples. 
He said to them,
“Did you receive the Holy Spirit when you became believers?”
They answered him,
“We have never even heard that there is a Holy Spirit.”
(Acts 19:1-8)

Even though believers may have no idea about the work of the Holy Spirit, the Spirit is still at work!