"And thoughts descend to words."
In this poem, the thought of immortality pleases the narrator, but, at the same time, he realizes that nothing can last for ever. Taking into consideration that an idea is what can bring immortality into existence, he thinks up this line. Once a thought is partially lost, it is put into words, where its true essence can never be completely captured.
"Love like your own, that may survive
Long after yours has ceased to burn."
Love can be a dangerous thing, as discovered and conveyed by the narrator of this short poem. The specific wording on love "ceasing to burn" are most likely used to show that being in love feels like a fire, but losing it is also like extinguishing a great flame.
"A continent upon my back,"
Of course, the narrator is not literally carrying a continent upon his or her back, but he or she feels such a sensation. When in times of great hardship, it is easy to try to seek escape, like the poems title, but sometimes it is not possible.
