According to the Bible, the red heifer a reddish-brown cow, probably no more than two years old which had never had a yoke on it was to be sacrificed as part of the purification rites of the Mosaic Law. The slaughtering of a red heifer was a ceremonial ritual in the Old Testament sacrificial system, as described in Numbers 19:1-10. The purpose of the red heifer sacrifice was to provide for the water of cleansing (Numbers 19:9), another term for purification from sin. After the red heifer was sacrificed, her blood was sprinkled at the door of the tabernacle.
The imagery of the blood of the heifer without blemish being sacrificed and its blood cleansing from sin is a foreshadowing of the blood of Christ shed on the cross for believers' sin. He was "without blemish" just as the red heifer was to be. As the heifer was sacrificed "outside the camp" (Numbers 19:3), in the same way Jesus was crucified outside of Jerusalem: "And so Jesus also suffered outside the city gate to make the people holy through his own blood" (Hebrews 13:11-12).
The Bible does teach that one day there will again be a temple of God in Jerusalem (Ezekiel chapters 41-45). Jesus prophesied that the antichrist would desecrate the temple (Matthew 24:15), and for that to occur, there obviously would have to be a temple in Jerusalem once again. Many anticipate the birth of a red heifer because in order for a new temple to be sanctified along with the Cohen, according to the Old Testament law, a red heifer would have to be sacrificed for the water of cleansing used in the temple. So, when a red heifer is born (which is quite unusual) it might be a sign that the temple will soon be rebuilt.