It means never changing or altering one's commitment or loyalty from beginning to end. It describes unwavering persistence.
渝改变，违背。自始自终一直不变。指守信用。
《晋书·谢安传》安虽受朝寄，然东山之志始末不渝，每形于言色。”
She remained loyal to her principles throughout her career, never wavering.
Learn the next connected idiom: 始终不渝 (shǐ zhōng bù yú) → 余波未平 (yú bō wèi píng)
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