مَطْهَرَةٌ لِلْفَمِ points to cleanliness of the mouth. Caring for teeth, preventing unpleasant breath, and considering others when speaking are part of good social conduct.
مَرْضَاةٌ لِلرَّبِّ brings out the devotional dimension. Worship is not limited to large, exceptional actions; routine cleanliness can also be pursued with the desire for Allah’s pleasure.
Cleanliness should not become mere outward display, while religious intention is not an excuse to neglect practical cleanliness. Both dimensions strengthen the practice.