This was not made known to people in other generations as it is now revealed to His holy apostles and prophets by the Spirit:Ephesians 3:5 HCSB

It was Paul's job to teach others what was revealed to him. And it is our job to teach what is revealed to us. 

Then Jesus came near and said to them, “All authority has been given to Me in heaven and on earth.  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 everything I have commanded you. And remember, I am with you always, to the end of the age.”

Matthew 28:18‭-‬20 HCSB

https://bible.com/bible/72/mat.28.18-20.HCSB

And what you have heard from me in the presence of many witnesses, commit to faithful men who will be able to teach others also.

2 Timothy 2:2 HCSB

https://bible.com/bible/72/2ti.2.2.HCSB

The hidden things belong to the Lord our God, but the revealed things belong to us and our children forever, so that we may follow all the words of this law.

Deuteronomy 29:29 HCSB

https://bible.com/bible/72/deu.29.29.HCSB

The most basic teaching comes in one-on-one discipleship. This is the model of Jesus with Peter, James, and John. He spent most of His time alone with them. This is the idea behind the great commission that we are to make disciples of all nations. This is the command to all Christians. This is the teaching model used by Paul with Timothy, Titus, and Onesimus.

I appeal to you, instead, on the basis of love. I, Paul, as an elderly man and now also as a prisoner of Christ Jesus, appeal to you for my son, Onesimus.  I  fathered him while I was in chains. Once he was useless to you, but now he is useful both to you and to me. I am sending him back to you as a part of myself.

Philemon 1:9‭-‬12 HCSB

https://bible.com/bible/72/phm.1.9-12.HCSB

Another way we are to teach is to be a group leader. This is how Jesus interacted with the 12. He would spend time alone with them teaching and explaining the hidden things of the crowd to them. This is the method behind Paul meeting with anyone who would hear him after He gets thrown out of the synagogue. The idea here is that they get a little less of the one-on-one insight, but it is also a personalized time. This would be compared to a house church these days. 

On the first day of the week, we assembled to break bread. Paul spoke to them, and since he was about to depart the next day, he extended his message until midnight. There were many lamps in the room upstairs where we were assembled,

Acts 20:7‭-‬8 HCSB

https://bible.com/bible/72/act.20.7-8.HCSB

So he left there and went to the house of a man named Titius Justus, a worshiper of God, whose house was next door to the synagogue. Crispus, the leader of the synagogue, believed the Lord, along with his whole household. Many of the Corinthians, when they heard, believed and were baptized.

Acts 18:7‭-‬8 HCSB

https://bible.com/bible/72/act.18.7-8.HCSB 

The third way that we can teach is to be a teacher. A Sunday school would fall into this category. Jesus did this kind of teaching with the 70 disciples. The idea is less personal and more formal. Paul's example would be when he was a professor in the school of Tyrannus.

But when some became hardened and would not believe, slandering the Way in front of the crowd, he withdrew from them and met separately with the disciples, conducting discussions every day in the lecture hall of Tyrannus.  And this went on for two years, so that all the inhabitants of Asia, both Jews and Greeks, heard the message about the Lord.

Acts 19:9‭-‬10 HCSB

https://bible.com/bible/72/act.19.9-10.HCSB

The last way that we are to teach would be to the masses. Think of a pastor or evangelist. Jesus did it with all the people around him whether from a boat, on a hill, or in the temple or synagogue. This was how Paul would teach each sabbath to the jews. 

Back to the great commission. One-on-one is our Jerusalem. Jerusalem is our innermost closest people. The group leader would then become our Judea. Judea is a bigger group of close acquaintances. The teacher would be like Samaria. Samaria is our influence among a larger group of people. The ends of the earth become Pastors and Evangelists. 

In the day of mass communication and social media, God's plan for raising up disciples and followers of Him is one-on-one discipleship. And He uses every other form of teaching to reach out with His word. "Brian's Quiet Time Thoughts" is a tool God can use to reach out to 12, 70, or a great multitude, but it will never replace the individual aspect of One-on-one discipleship.