4 ideas
Tsvetaeva argues to Rilke that no poet truly writes in a mother tongue, because composing poetry is itself translating from an inner, pre-verbal language into a spoken one. On this view, writing to him in German, a language not her own, is not a handicap but a visible version of what every poem does. A poet's native language is poetry itself, not French, German or Russian.
Pasternak, devoted to Rilke, asks him to send his books to Tsvetaeva, and her correspondence with Rilke then quickly outgrows his own. When she makes clear she wants that exchange for herself, Pasternak withdraws and stops writing to Rilke. The person who creates a connection between two others can lose his own place in the bond he made.
Tsvetaeva treats the letter as the medium where love is fullest, because absence removes the friction and disappointment of bodies, habits and circumstances. A physical meeting is endlessly proposed and deferred, since meeting risks shrinking a relationship that exists most intensely in writing. The meeting that never happens keeps the bond at full strength.
Rilke never fully disclosed his worsening illness, and his letters thinned and stopped months before he died in December 1926. Tsvetaeva answered his death not with silence but with another letter, the poem 'New Year's Letter', addressed to him as if he could still read it. A relationship built entirely on correspondence can continue past death, because death changes only whether replies come, not whether address is possible.