“ וְלָקַח אֶלְעָזָר הַכֹּהֵן, מִדָּמָהּ–בְּאֶצְבָּעוֹ; וְהִזָּה אֶל-נֹכַח פְּנֵי אֹהֶל-מוֹעֵד, מִדָּמָהּ–שֶׁבַע פְּעָמִים”
“And Eleazar the priest shall take some of its blood with his finger, and sprinkle some of its blood toward the front of the tent of meeting seven times.”
The Zohar reveals that everything related to the Red Heifer was done with the aspect of seven. It is done so because Malchut is included from the seven sefirot of Chessed to Malchut. Because the vessel of Malchut has the ability to reveal all the seven sefirot the process must cover all of them to purify the vessel. The holiday of Sukkot and Passover have seven days so the light of the holiday would impact the whole vessel.
The entire process was for purification and not as the High priest does for holiness, which is drawing Light from Binah to Malchut.
After the Red Heifer was slaughtered and on fire the priest would add several elements that are related to red and or to the aspect of seven.
Some of the Red Heifer ashes were placed on a plate and washed with water into a vessel. These waters were used to purify those who were in need.
The sages tells us (משנה תורה, ספר טהרה, הלכות פרה אדומה)
“ותשע פרות אדומות נעשו משנצטוו במצוה זו, עד שחרב הבית בשנייה–ראשונה עשה משה רבנו, ושנייה עשה עזרא, ושבע מעזרא עד חורבן הבית; והעשירית עושה המלך המשיח, מהרה “ייגלה
Moses processed the first Red Heifer. It was enough until the destruction of the first Holy Temple. Ezra the scribe did one for the second Holy Temple. Until its destruction they had seven more Red Heifers and all together nine. The tenth will be done by the Mashiach to cleanse and purify the entire world.
May it be soon, Amen.