同 gathers a mouth 口 under a covering frame — everyone under one roof saying the same thing. Sameness as chorus: the character has meant 'together, alike' since the bronze inscriptions.
同 builds belonging: 同学 (classmate — 'same-study', with 学), 同事 (colleague — 'same-work'), 同意 (to agree — 'same-mind'). Address a stranger's group as 同学们 and you've made a room of allies. The grand old ideal 大同 — 'Great Unity' — is Confucius's utopia where the world is shared by all; it still names streets and districts across China.
One frame, one voice from every mouth 口 — the SAME, TOGETHER.
大同 (Great Unity), Confucius's utopia, names a major city in Shanxi — you can buy a train ticket to Utopia.