In an introductory lecture note by T. Saito,

http://www.ms.u-tokyo.ac.jp/~t-saito/pp/GR2.pdf

he said that the absolute Galois group $\text{Gal}(\bar{\mathbb{Q}}/\mathbb{Q})$ could be seen as the fundamental group of the set set of primes $2,3,5,... \infty$. The local systems over $2,3,5,... \infty$ could be seen as determined by the representations of $\text{Gal}(\bar{\mathbb{Q}}/\mathbb{Q})$. Could anyone elaborate on this analogy? In what sense does the analogy catch the essence of Galois representations?