John 16:22 "Therefore you now have sorrow; but I will see you again and your heart will rejoice, and your joy no one will take from you."
This was the last sermon of our Lord Jesus Christ to His disciples, for He knew that none of them were saved for they did not believe that He was the sacrificial Lamb for the propitiation of their sins. They would be sorrowful as soon as they saw the Lord Jesus their King of Israel arrested (God being arrested) which is beyond comprehension.
John 6:68-69 But Simon Peter answered Him, "Lord, to whom shall we go? You have the words of eternal life. Also we have come to believe and know that You are the Christ, the Son of the living God."
Though the disciples believed and confessed Him as the Messiah, the Son of the living God (demon possessed also confessed that), they were not saved nor born again and without the indwelling of the Holy Spirit. The Holy Spirit can only be given to born again Christians, who had repented of their sins, believed and accepted Jesus' death for the propitiation of their sin, His victory over death in Hades, His glorious resurrection from the dead to the glory of the Father in heaven.
Luke 4:41 And demons also came out of many, crying out and saying, "You are the Christ, the Son of God!" And He, rebuking them, did not allow them to speak, for they knew that He was the Christ.
Note: that even the unsaved (many with demons and unclean spirits) also confessed Jesus as the Christ, the Son of God.
Mark 1:23-24 Now there was a man in their synagogue with an unclean spirit. And he cried out, saying, "Let us alone! What have we to do with You, Jesus of Nazareth? Did You come to destroy us? I know who You are—the Holy One of God!"
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.
Our Lord told them that soon they would be sorrowful because of their ignorance of the understanding of Scriptures. The death of our Lord is out of His great love for us as the propitiation of our sins and yet they were sorrowful for His sacrificial love. It was only after the Lord's revelation and fellowship with them in Galilee, that they understood the gospel and rejoiced for their redemption in His death and resurrection. After that they were filled with the joy and gratitude of the Lord and they praised and worshipped God continuously. Having been filled with the power of the Holy Spirit they joyfully bear witness to the everlasting gospel. These were the disciples of our Lord Jesus Christ.
But we can't say this with the disciples of those preaching the diluted or perverted gospel. These are not saved even though they were told that they are the children of God. Without the Holy Spirit dwelling in them, they will not be able to understand the truth in the word of God. Until they repent of their sins and worldliness, they will not be able to understand the salvation through blood of the Lamb of God and they will be lost forever.
Therefore, brethren, we are debtors—not to the flesh, to live according to the flesh. For if you live according to the flesh you will die; but if by the Spirit you put to death the deeds of the body, you will live. For as many as are led by the Spirit of God, these are sons of God. (Rom 8:12-14)