。
A mother's love is greater than any other.
Literal
Mother [gen-の] love [topic-は] others [than-よりも] great is.
よりも is よりも (より + emphatic も) — 'more than' with added stress. The copula である is the literary/formal counterpart of だ or です, common in essays, formal writing, and aphoristic statements. Combined, the sentence has a written, slightly elevated feel, fitting its aphoristic content.