请 (traditional 請) joins the speech radical 讠 with 青 (green, the color of clarity and purity, also the sound). Speech made pure and gracious — a request, an invitation.
请 opens every polite sentence in Mandarin: 请问 (may I ask — with 问 you learned), 请坐 (please sit — with 坐), 请进 (please come in — with 进). It also means to treat: 我请你 ('I invite you') is the magic phrase for picking up the bill. Chinese hospitality wars are fought with 请 — whoever says it first pays, and everyone fights to say it first.
Speech 讠 kept green-pure 青 — courteous words: PLEASE.
At a Chinese dinner, 我请 ('my treat') triggers a friendly wrestling match for the bill — losing means letting the other pay.