Mal 4:5 "Behold, I will send you Elijah the prophet before the coming of the great and dreadful day of the LORD."
This was the day when our Lord Jesus was crucified and died on the cross.
Note - Elijah came as John the Baptist
Mat 26:50 And Jesus cried out again with a loud voice, and yielded up His spirit.
The Dreadful Day of the Lord
Mat 27:51a Then, behold, the veil of the temple was torn in two from top to bottom;
At the death of our Lord Jesus, the veil was torn in two, signifying that Yahweh Himself had destroyed the temple of God thereby ending the 'Old Covenant' of Judaism with abolishment of the priesthood, temple sacrifices, worship, etc. This was the dreadful day of the Lord for all Israelites and Jews, for they are no longer the people of God since they had put themselves under the curse of shedding the innocent blood of the Messiah, Son of God.
Mat 27:25 And all the people answered and said, "His blood be on us and on our children."
The Great Day of the Lord
1Cor 6:19-20 Or do you not know that your body is the temple of the Holy Spirit who is in you, whom you have from God, and you are not your own? For you were bought at a price; therefore glorify God in your body and in your spirit, which are God's.
After His resurrection, our Lord Jesus having poured out His previous blood on the cross for all mankind, started the New Covenant by giving His Holy Spirit to dwell in His disciples thus making the physical body of every believer to become the temple of God.
Rocks praising the Lord
Mat 27:51b and the earth quaked, and the rocks were split,
However, all His disciples mourned His death instead of thanking and praising God and rejoicing for the greatest love ever shown to mankind by the love of the Son of God dying on the cross. As God prophesied, since His disciples did not praise His great love for them on the cross, He made the rocks to praise Him by splitting.
Luke 19:38-40 saying: " 'Blessed is the King who comes in the name of the LORD!' Peace in heaven and glory in the highest!" And some of the Pharisees called to Him from the crowd, "Teacher, rebuke Your disciples." But He answered and said to them, "I tell you that if these should keep silent, the stones would immediately cry out."
The blood of animals
Heb 10:4 For it is not possible that the blood of bulls and goats could take away sins.
The sins of the saints of old (including Samuel) under Moses law were only covered by the blood of animals, so they were all held in Sheol until their redemption.
1Sam 28:11,15a Then the woman said, "Whom shall I bring up for you?" And he said, "Bring up Samuel for me."... Now Samuel said to Saul, "Why have you disturbed me by bringing me up?"
The precious blood of Jesus
Eph 1:7 In Him we have redemption through His blood, the forgiveness of sins, according to the riches of His grace.
All these saints need the precious blood of Jesus for the propitiation of their sins. At the crucifixion of our Lord, His precious blood replaced the blood of animals which by faith they offered to God. So at His resurrection, the saints too were raised from the dead by His Spirit and be with the Lord in heaven. Thank God that now when a born again Christian dies, he goes straight to heaven.
Mat 27:52-53 and the graves were opened; and many bodies of the saints who had fallen asleep were raised; and coming out of the graves after His resurrection, they went into the holy city and appeared to many.