“In the upper room on the night of the Passover, Jesus decided that the great mystery of the Trinity was the teaching His disciples most needed to hear (cf. John 13-17). Why was this truth so important? Because Jesus wanted His disciples, and us, to come to know God, in all the riches and fullness of His being.
He wanted us to know God in His eternal glory and to recognize how great He is; but He also wanted us to see that the God whose being we cannot comprehend is also the God who is a Father who loves us, a Son who came to die for us, a Spirit who brings us into God’s heart and who brings God into our hearts.
On that night in which He was betrayed, Jesus preached the doctrine of the Trinity to His disciples because He knew that in the last analysis, only the people who know their God can stand firm in days of trial.
As you study the biblical teaching on God’s character and work, remember that He is not a distant God, but One whose inner being was revealed by Jesus in the most critical hours of His life on earth.
And pray that this Three Personed God will reveal Himself more fully to you through Scripture, that you may come to know Him — in the knowledge that is eternal life (John 17:3). Search for this knowledge with all your heart.”
–Sinclair B. Ferguson, A Heart For God (Carlisle, PA: Banner of Truth, 1987), 22-23.