When preparing a lesson or a sermon - sometimes I used to find myself just paralyzed, waiting for "guidance" as to what scripture, what words to say and use. On the other hand, when preparing a lesson from a scripture already chosen, the ideas and insights will just flow, and as I work to get them together, there will come a calm assurance of the Lord's participation in the result. Sure, the Lord has given me explicit direction in advance a time or two but those occasions are rare - rather, its normal to prepare in a workmanlike fashion and find that the Lord is blessing me as I put things together.
And then there are those precious moments when He just surprises us all with His giving of an insight and a revelation.
By way of example, once I was teach a passage on prayer and we were talking about why God wants us to pray for others. After all, He already loves them, and He already knows we love them also .. what's the purpose of suggesting we pray? So in my human wisdom (as it seemed when I started the thought) I speculated out loud for the class, well, perhaps its because He wants us to have a share in the giving of blessings, so He reserves some blessings to be released by our prayers for others. And as I just mentioned this by way of speculation, there came an overwhelming sense of the presence of God assuring me, YES, THAT'S IT! and I had to pause, I couldn't even continue for a couple of seconds, it was such an overpowering moment . . .
That's the way it goes, as far as I know. So I quit worrying about selection of the text and main points. Just pick something reasonable and trust the Lord to infuse His word with His Spirit.