What did Jesus promise that the Holy Spirit would do?
"Howbeit when he, the Spirit of truth, is come, he will guide you into all truth." John 16:13.
How much truth?
When would that happen?
"When he, the Spirit of truth, is come."
The Holy Spirit came on the day of Pentecost, as recorded in Acts chapter 2. Jesus' promise was that when the Holy Spirit came, He would guide the church into all truth. The knowledge of truth would not be withheld for hundreds of years after Pentecost, but would come "when he, the Spirit of truth, is come." This means that we should be able to see all truth present in the early apostolic church.
And that is exactly what the book of Acts records. Here is a list of doctrinal truths that were understood in the days of the apostles.
The role of the Scriptures -- Acts 17:11
God -- Acts 24:14
Jesus -- Acts 9:20
Salvation -- Acts 26:18
The second coming of Jesus -- Acts 1:11
The non-immortality of the soul -- Acts 2:29, 34
The resurrection of the dead -- Acts 24:15
An appointed date for the judgment -- Acts 17:31
The cleansing of the sanctuary -- Acts 3:19
The law of God -- Acts 22:12
The seventh-day Sabbath -- Acts 16:13
The church -- Acts 2:47
Spiritual gifts -- Acts 21:8-10
Healthful living -- Acts 24:25
Baptism -- Acts 8:12
What topics did Paul confidently emphasize in his preaching and teaching?
"Preaching the kingdom of God, and teaching those things which concern the Lord Jesus Christ, with all confidence, no man forbidding him." Acts 28:31.
Did he leave out any important matters?
"And how I kept back nothing that was profitable unto you, but have shewed you, and have taught you publickly, and from house to house." Acts 20:20.
"For I have not shunned to declare unto you all the counsel of God." Acts 20:27.
What were the results of Paul's thorough teaching?
"And so were the churches established in the faith, and increased in number daily." Acts 16:5.
Of what did Paul warn the elders of the church?
"For I know this, that after my departing shall grievous wolves enter in among you, not sparing the flock. Also of your own selves shall men arise, speaking perverse things, to draw away disciples after them. Therefore watch, and remember, that by the space of three years I ceased not to warn every one night and day with tears." Acts 20:29-31.
Similar warnings about the introduction of false doctrine were given in 2 Thessalonians 2:3-12; 2 Peter 2:1-3; and Jude 3, 4. The church would have to go through a period of terrible apostasy.
But "the times of refreshing" to come would also be "the times of restitution of all things." Acts 3:19, 21. All truth would be fully restored at last.
See also Daniel 8:9-14.