Te-form of verb+adjective, what grammar is it in Japanese language?

Question:

For example読んで良かった in あなたが読んで良かった本は? Why is 読んで used instead of 読んだ?

Answer:

1. Why does it matter? Why are you　looking for some sort of cosmic reason? Because that's the way it is, man.
What grammar is it? Ummm....Japanese grammar?


When you are using the verb +yokatta, you are connecting one part of the sentence to the other. The verb or adjective you use is presented as being part 1, and the outcome is part 2

kasa o motte kite, yokkata. It was good that I brought an umbrella. With the -te form, you can see that the first clause is connected to the adjective.

if you said
kasa o motte kita. Yokatta. You are developing ideas one at a time, like a two or three year old does.
The ability to synthesize your speech and draw conclusions based on actions is part of the job of the te form, why? I don't know, but I think it has something to do with Shinto and green tea and wabisabi and hello kitty.