Ideas that make the message less wise (6)
I believe the answer is:
themes
'ideas that' is the definition.
'themes' can be an answer for 'ideas' (theme is a kind of idea). I'm unsure of the remainder of the definition.
'the message less wise' is the wordplay.
'less' is a deletion indicator.
'wise' becomes 'sage' (similar in meaning).
'message' with 'sage' taken away is 'mes'.
'the'+'mes'='THEMES'
'make' is the link.
Can you help me to learn more?
(Other definitions for themes that I've seen before include "Motifs, subjects" , "items proposed for discussion" , "Subjects or repeated melodies" , "Subjects or unifying ideas" , "'Subjects, topics (6)'" .)