John 14:25-26 "These things I have spoken to you while being present with you. But the Helper, the Holy Spirit, whom the Father will send in My name, He will teach you all things, and bring to your remembrance all things that I said to you.
When the Helper comes, He will teach us all the things, which He brings back to our remembrance the words spoken by our Lord in the bible.
Luke 24:44-47 Then He said to them, "These are the words which I spoke to you while I was still with you, that all things must be fulfilled which were written in the Law of Moses and the Prophets and the Psalms concerning Me." And 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.
So before His Ascension, He explained to them the gospel. Our Lord then told them to wait in Jerusalem for the promise of the empowering by their baptism with the Holy Spirit.
Acts 2:36-38 "Therefore let all the house of Israel know assuredly that God has made this Jesus, whom you crucified, both Lord and Christ." Now when they heard this, they were cut to the heart, and said to Peter and the rest of the apostles, "Men and brethren, what shall we do?" Then Peter said to them, "Repent, and let every one of you be baptized in the name of Jesus Christ for the remission of sins; and you shall receive the gift of the Holy Spirit."
Immediately after their baptism with the Holy Spirit, the disciples were filled with understandings, truth, power, etc. and Peter (timid and unlearned fisherman) then preached his anointed gospel message, which convicted the devoted Jews to repentance.
John 16:13 "However, when He, the Spirit of truth, has come, He will guide you into all truth; for He will not speak on His own authority, but whatever He hears He will speak; and He will tell you things to come."
Only after we have kept His words can Jesus baptise (immerse) us with the Spirit of truth sent by the Father. Jesus is the way, the truth, and the life (John 14:6). Then truly we are born again with His Spirit in complete control of our spirits.
Gal 2:20 I have been crucified with Christ; it is no longer I who live, but Christ lives in me; and the life which I now live in the flesh I live by faith in the Son of God, who loved me and gave Himself for me.
He will tell you things to come
The Spirit of truth will also tell us the things in the future by helping us to understand the teachings of end time events as recorded in the bible, if we are now living in the last days. No wonder, our Lord Jesus spent so much time warning us by giving in great details the persecutions, tribulations, wars, pestilences, deceptions of the false christs, false prophets and the Antichrist, etc. before Rapture (His appearance in the cloud to collect His elects). So brethren, let us understand the end time events and teach them to our sheep, so that their faith will be strengthened when the Spirit of truth brings them back to their remembrance.
Brethren, until our Lord Jesus baptize us with the Holy Spirit, we will not be able to understand end time prophecies and events. Without the Spirit of truth leading us, we will easily be deceived by false teachers, false prophets and the Antichrist in the last days.