With the events of the Passion Week, Matthew is very deliberate to note and capture testimony.
In Matthew 27:51-56, he records the testimony of the soldiers and the women that were present for the crucifixion. In Matthew 27:57-61, under the watchful eyes of those women the body was moved to the stone-closed tomb. In Matthew 27:62-66, the tomb was sealed and guarded.
Then in Matthew 28:1-10, after dual-Sabbaths (sabbaton is plural, the high day (John 19:3) that starts the week-long feast of Unleavened Bread (Thu/Fri) is followed by the weekly Sabbath (Fri/Sat)), the women go on the first day of the week to embalm the body without a plan to open the tomb.
They found the tomb open and the guards gave them testimony of how the angel opened the tomb. Then the angel bid them to enter the tomb and see the place where Jesus had lain. No aspect of the events should be missed. All must be witnessed. The angel instructed them:
“Do not be afraid, for I know that you seek Jesus who was crucified. He is not here, for he has risen, as he said. Come, see the place where he lay. Then go quickly and tell his disciples that he has risen from the dead, and behold, he is going before you to Galilee; there you will see him. See, I have told you.”
Then Jesus himself appears and confirms the instruction.
“Do not be afraid; go and tell my brothers to go to Galilee, and there they will see me.”
But instead out of fear they locked themselves in a room that night and waited for Thomas to arrive (John 20:19-25). There Jesus appeared again and repeated the core of his teachings:
Jesus said to them again, “Peace be with you. As the Father has sent me, even so I am sending you.” And when he had said this, he breathed on them and said to them, “Receive the Holy Spirit. If you forgive the sins of any, they are forgiven them; if you withhold forgiveness from any, it is withheld.”
Then with "Doubting Thomas" in tow, they obeyed and went to Galilee. If they were vocal and obedient about the command, this may have been where more than 500 disciples gathered to see the risen Christ (1 Corinthians 15:3-8).
Now the eleven disciples went to Galilee, to the mountain to which Jesus had directed them. And when they saw him they worshiped him, but some doubted.
They went to "the" mountain, possibly the very one where His ministry began, where He delivered the Beatitudes; where He spoke as one with "authority" (Matthew 7:29); from where He began a ministry validated by miracles demonstrating that authority (Matthew 8:9, Matthew 9:6, Matthew 9:8).
But this day He declares His authority. The verb "given" (didōmi) is in the aorist tense and translators vacillate between using present or past tense in English, because it is not done with respect to time. This authority is rooted in eternity and His identity.
And Jesus came and said to them, “All authority in heaven and on earth has been given to me. Go therefore and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, teaching them to observe all that I have commanded you , , ,
With this authority, He commands them to make disciples and baptize them in "the" name (singular) of the Triune God. There is only one name. God revealed it in Exodus 3:14 as the great "I AM"; the self-existent eternal one (Yᵊhōvâ)
In the line that follows, Jesus declares His identity by using that name:
And behold, I am with you always, to the end of the age.”
He did not say "will be with you". The verb "am" (eimi) is in present tense and is stretched across all time (See for example John 8:56-59). Something a simple man cannot do. In this phrase He declares Himself to be the Son of God.
Eight days later (length of a round trip to Galilee) they once again lock themselves in the room in Jerusalem (John 20:24-29). This time with Thomas. Jesus once again appears to them and invites Thomas to touch His wounds.
Thomas could only reply “My Lord and my God!”.