John 20:17 records this account: “Jesus said unto her, Touch Me not; for I am not yet ascended to My Father: but go to My brethren, and say unto them, I ascend unto My Father, and your Father; and to My God, and your God.”
Christ was a holy sacrifice, the first human being to be resurrected to eternal life. His death (as the sacrifice for our sins) was symbolized in ancient Israel by the Wave Sheaf offering, which was offered at the beginning of the Spring harvest (Lev. 23:10-12). This duty was to be carried out only by the High Priest. If it were handled by anyone other than the High Priest, the offering would have been defiled (impure), rendered unacceptable to God.
At the time Mary Magdalene saw Christ, He had not yet ascended to Heaven to be accepted by God the Father. Since Christ was the Wave Sheaf offering and is our New Testament High Priest (Heb. 9:11-12), no one could touch Him before He ascended.