Yes, as you said was true of John MacArthur - all the personal Bible study required for his writing his commentaries on Matthew (were necessary and helpful in the process), and also for the sermons he preached on about the book of Matthew! And as you say, when interacting with other Christians in Bible discussion - it is helpful to look up verses on whatever subject is talked about - each time, throughout the process. That way, it helps ensure that one is as correct as is possible, and it also helps to refresh his memory on it - plus he may learn additional things too - since that's always a possibility - the more we read and study God's Word!
Thanks for the compliment! You're right! I think I and my grand children are both a blessing to each other! And it is a blessing - after children are married and gone from home - to still have ways to be useful for God in our later part of life! No one likes to be useless, I'm sure!