This is the workhorse Montserrat pairing, and it works because the two faces are built on the same proportions from opposite sides of the sans/serif line. Merriweather was drawn for screen reading with a deliberately tall x-height, so it sits at almost the same height as Montserrat — the headings and body read as one sized system, not two mismatched fonts. The class contrast (geometric sans over a sturdy, slightly old-style serif) gives you hierarchy for free, while Merriweather's editorial warmth softens Montserrat's geometric coolness.
This is the workhorse Montserrat pairing, and it works because the two faces are built on the same proportions from opposite sides of the sans/serif line. Merriweather was drawn for screen reading wit...