Choose the grammatically correct sentence-

The correct answer is Option (3) - The important lessons are as followS

The grammatically correct sentence is: The important lessons are as follows.

"As follows" is the correct phrase to use when listing items or points that follow after the statement.

"As following" is incorrect because "following" is not used as a prepositional phrase in this context.
"As follow" is incorrect because it does not agree with the plural subject "lessons".