On speculating about God's eternal foreknowledge and election...

Our curiosity always has greater pleasure in giving itself to these matters than with what God has revealed to us about this matter in His Word.  We cannot harmonize God's revelation with our reason, which we have not been commanded to do anyway.

There is no doubt that God foresaw before the time of the world, and still knows, exactly, which people who are called will believe and which will not believe.  He also knows which of the converted will persevere and which will not persevere.  He knows which will return after a fall and which will fall into stubbornness.  He also knows the number of how many there are on either side.  Beyond all doubt this is perfectly known to God.  However, God has reserved this mystery for His wisdom.  He has revealed nothing to us about it in His Word, much less commanded us to investigate it with our thoughts.  Instead, He has seriously discouraged us from that.  Therefore, we should not reason in our thoughts, draw conclusions, or inquire curiously into these matters, but we should cling to His revealed Word, to which He points us.

~BOC, FSD, XI, 53-55