Does our response to the gospel catch God by surprise?
No. God knew from eternity past what we would do. When a person responds to the gospel, it does not catch Him by surprise; He already knew. As with Lydia, the Lord opened her heart, and her response was known beforehand. God's foreknowledge means our acceptance or rejection is not unexpected to Him.
Les explains that the call goes out to all, but only those who respond are chosen, like kids coming to the ball diamond. Lydia's heart was opened by the Lord, yet she still could have refused. Les says God knew from eternity past what we would do, so when Lydia responded, the Lord shouted across heaven, 'I knew she would.' It wasn't catching Him by surprise. We still have the option to respond or reject, but God's foreknowledge means our choice is never a surprise to Him.