[8:18] 1 tn Or “Therefore pay close attention”; Grk “Take heed therefore how you hear.”
[8:18] 2 tn Grk “and.” Here καί (kai) has been translated as “but” to indicate the contrast present in this context.
[8:18] 3 sn The phrase what he thinks he has is important, because it is not what a person thinks he has that is important but whether he actually has something or not. Jesus describes the person who does not heed his word as having nothing. The person who has nothing loses even that which he thought was something but was not. In other words, he has absolutely nothing at all. Jesus’ teaching must be taken seriously.
(NT only) to listen to the NET Bible 
