Using the word propose in the abstract I wrote a paper. In the last sentence of its abstract, I wrote: Finally, we propose.... 

Now, one of the reviewer's said that 

"Last sentence of abstract: « we propose » without saying for what use makes the sentence weird."

I can not understand what is the problem of using the phrase  « we propose ».

Thanks for any suggestions
It's very likely that the problem is not "we propose", it's whatever follows. Apparently you said "we propose X" and the reviewer thinks that you should explain why you propose X.