。
I only go to church out of a sense of duty to my mother.
Literal
Mother [toward-に対する] duty [only-by-だけで] church [to-に] go (polite).
~に対する is a pre-nominal modifier meaning 'toward X' or 'against X' — a more formal, written alternative to ~への. Here 'duty toward mother.' The composite だけで ('only with,' 'solely because of') presents the duty as the sole reason for going. The sentence is carefully structured to downplay any personal faith — attendance is framed as obligation, not belief.