Mark states that the reason was so that they would be “with Him, and that He could send them out to proclaim (my translation, preach is overused for that Greek word).
Now consider the passage I mentioned yesterday, Deuteronomy 17:14 – 20. The King of Israel is to make a handwritten copy of the Law and he is to keep it “with him”. In the Septuagint, the Greek version of the OT, the Greek, with him, is the same as in Mark 3:14. Is this significant? It seems to be.
The Israeli king is to lead the kingdom, to do so in the way his Lord intended. In order to do so he needed to be intimately acquainted with whom he was to represent, he needed to know and fear his Lord. To do that he needed constant exposure to the Word, Law, of his Lord.
The twelve were the foundation stones of the Church. They were the initial leaders, movers, and shakers of that Body. As such they needed to be intimately acquainted with whom they were to represent. They needed to be intimately exposed to His life; and they were for three years.
Do you see the parallel? To know God, to be prepared to lead, one must be really close to God, to know Him well. We can no longer walk with Jesus physically as the 12. But we have more than the Law. We have the prophets, the writings, the Gospels, the Epistles, and Revelation.
We must as the king, be with Him in His Word, daily. That is our chief source of knowing Him well…