Perhaps you mean ..
Assuming data to be added is within B1:B141
(ie you want:=B1+B15+B29+...+B141)
In say, C1:
=SUMPRODUCT(--(MOD(ROW(A1:A141)-1,14)=0),B1:B141)
Or perhaps you were hinting at something like this ..
In any starting cell, say in E2:
=IF(MOD(ROW(A1)-1,14)=0,"Std Msg","")
Copy E2 down as far as required to insert the phrase: Std Msg
in E2, E16, E30, etc