It has to go back on the tenth (5)
I believe the answer is:
tithe
'tenth' is the definition.
(a tenth of one's income given to a church)
'it has to go back on the' is the wordplay.
'it' becomes ''t' (abbreviation. e.g. in 'tis).
'has' says to put letters next to each other.
'to go' becomes 'ith' (I can't justify this - if you can you should believe this answer much more).
'back on' says to take the final letters (the letter at the back).
The last letter of 'the' is 'e'.
't'+'ith'+'e'='TITHE'
Can you help me to learn more?
(Other definitions for tithe that I've seen before include "property tax" , "Tenth (of one's earnings)" , "Levy of one tenth of something" , "Tenth part paid to a church" , "Tenth of income given to church" .)