holy, saint, sage, master, priest
聖 centers on a person of exceptional wisdom, virtue, or sacred status: a sage, saint, or holy master. The priest sense is a natural extension of that sacred authority.
聖 combines 耳 (ear) and 口 (mouth) with 王 (king), suggesting a person who listens, speaks, and rules with wisdom. The exact historical development is uncertain, but the component combination is well established.
A king (王) who uses his ears (耳) and mouth (口) wisely becomes a sage or saint. Picture a holy master listening carefully and speaking truth.
For セイ, imagine a saintly figure saying 'say' as he preaches: 'say' -> セイ, and his holy words spread wisdom.
highly virtuous monk
Saint; St.; S.
Bible; the Scriptures; Holy Writ
holiness; sacredness; sanctity; dignity
(Confucian) temple; church; sanctuary
sacred place; holy ground; the Holy Land
saint
holy; sacred
esteemed profession (e.g. priest, monk, teacher, doctor, etc.); venerable vocation
sacred precincts; sanctuary; consecrated ground; holy ground
holy war; crusade
the Holy Ghost; the Holy Spirit
mother of a holy person
holy water
sacred fire; sacred flame
saint
saint; holy woman
sacred song; hymn; chant
great sage
Buddha