Acts 16:13 (NIV)
On the Sabbath we went outside the city gate to the river, where we expected to find a place of prayer. We sat down and began to speak to the women who had gathered there.
I conclude the situation is something like this:
Just before the writer sit down, there are already some women there. This situation I name it, time-frame-1. Time-frame-2 is after the apostles sat down then begin speaking to the women.
Acts 16:14a (NIV)
One of those listening was a woman from the city of Thyatira named Lydia, a dealer in purple cloth. She was a worshiper of God.
Next, I assume what the writer means (inspired by the Holy Spirit) in the bolded sentence is that Lydia already as a believer in the sight of God at time-frame-1 before time-frame-2.
Acts 16:14b (NIV)
The Lord opened her heart to respond to Paul's message.
The event "The Lord opened her heart" is either while Paul is talking (time-frame-2) or after Paul finished his talking. So, this event not happened at time-frame-1.
My question :
What does "The Lord opened her heart" mean according to Calvinists?