John 6:20 "Most assuredly, I say to you that you will weep and lament, but the world will rejoice; and you will be sorrowful, but your sorrow will be turned into joy."
The first part of this prophecy was fulfilled just hours later when He was arrested, scourged and sent to carry His cross of crucifixion. The second part was fulfilled after His resurrection from the dead.
Luke 23:27-28 And a great multitude of the people followed Him, and women who also mourned and lamented Him. But Jesus, turning to them, said, "Daughters of Jerusalem, do not weep for Me, but weep for yourselves and for your children."
As Jesus carried His cross in pain, He told those mourning and lamenting womenfolk not to weep for Him but for the wraths of God coming upon Jerusalem. He rejoiced in His sufferings, which He volunteered out of His love for mankind for by His stripes we are healed.
Mark 16:9-11 Now when He rose early on the first day of the week, He appeared first to Mary Magdalene, out of whom He had cast seven demons. She went and told those who had been with Him, as they mourned and wept. And when they heard that He was alive and had been seen by her, they did not believe.
His disciples mourned and wept because their hopes of power, riches, prosperity, etc. were over because the King of Israel was killed. Even though they were told that their King had resurrected, they did not believe it, for they witnessed the death of their King who must not die.
Mark 14:27-28 Then Jesus said to them, "All of you will be made to stumble because of Me this night, for it is written: 'I will strike the Shepherd, and the sheep will be scattered.' But after I have been raised, I will go before you to Galilee."
It was in Galilee that our risen Lord told them to cast their net on the right side and their net was filled with fish just as it was before His death. Then they ate and fellowshipped with the Lord and only then they believed Him
John 21:5-7a Then Jesus said to them, "Children, have you any food?" They answered Him, "No." And He said to them, "Cast the net on the right side of the boat, and you will find some." So they cast, and now they were not able to draw it in because of the multitude of fish. Therefore that disciple whom Jesus loved said to Peter, "It is the Lord!"
Luke 24:46-47 Now as He opened their understanding, that they might comprehend the Scriptures. Then He said to them, "Thus it is written, and thus it was necessary for the Christ to suffer and to rise from the dead the third day, and that repentance and remission of sins should be preached in His name to all nations, beginning at Jerusalem."
Only after the resurrection of Jesus in Galilee, they were able to understand the Scriptures and once again gave their lives to follow Jesus and preach the everlasting gospel, this time not for His earthly kingdom but for the eternal kingdom of Christ.
Luke 24:51-53 Now it came to pass, while He blessed them, that He was parted from them and carried up into heaven. And they worshiped Him, and returned to Jerusalem with great joy, and were continually in the temple praising and blessing God. Amen.
Having understood His love and eternal gospel, they were filled with joy seeing Jesus departing back to the Father in heaven. They eagerly awaited the baptism of the Holy Spirit by Jesus in Jerusalem so that they could minister just like our Lord Jesus, Who performed all types of signs and wonders according to the Father's will, taught the truth, and having great wisdom.