Better articulation in long slurred bows

Teaching student M on Merk, mm 24-25, his slurs were slow enough to cover all the notes. But the tone is sluggish. Two things: left hand's shift needs to be brisk and effort-less.

My new idea for explaining the character of the articulation in this spot is: An old and sick patient laying in the bed urging for some water and he says:'w-a-t-e-rr', without having much energy to speak he still tries to articulate to make people understand his need. This is portato! Portato in Italian means:'carried'!!

Practice the notes WITHOUT the bow, just the left fingers articulate each note with percussive approach.