Deer is the symbol of Christ, which means that Christ tramples and destroys the devil. Early orcs described stags as the ruthless enemies of snakes. They think the stag will chase snakes into their holes or crevices in rocks, submerge and devour them with breath or water from their mouths.
Because the snake is the symbol of Satan, stag often represents the Christian in the war between Christ and devil; The water used to wash the snake symbolizes the wisdom and purity of Christ, the gospel and the water flowing from the side where he was crucified.
It is also thought that a sick or old stag would hide the snake and swallow it. Then, the stag will drink a lot of water to overcome the poison of the snake, so as to restore its youth. The priest said Christians were saved because "when they are baptized, when they are cleansed of sin, the trace of sin disappears."
King David regarded stag as a symbol of the soul's desire to God. In Christian art, deer and deer's soul desire are purified through baptism and Holy Communion. Therefore, we can usually find it in baptism, the communion bar and the Grail.
Source: @aanthem