The wonders of the Trinity

Mention the Trinity and most Christians (including preacher-teachers) shrug their shoulders and say they can't explain him properly. That's a dreadful state of affairs in terms of our own faith and in terms of evangelism, and it's why I spent last week at Westminster College at the the Cambridge Summer School, run by Christian Heritage.
The speaker was Don Fairbairn, Professor of Historical Theology at Erskine Theological Seminary, South Carolina; a delightful and humble man with a golf handicap of less than 10!
Don's teaching reminded us of how the three persons of the Trinity each possesses the 'divine identity' (a phrase from Richard Bauckham). In other words the Father, the Son and the Holy Spirit each possess all of the characteristics of God-ness, and are therefore united as one God. No other real or imaginary god possesses these characteristics, and so there is only one true God.
But the really important aspect of Don's teaching was his emphasis on the relationship between the Father and the Son, and how, when we are united to Christ by faith, we share in this relationship. So, in John 13-17 Jesus reveals how we, as his redeemed people, can now and will in the future, share in the fellowship between the Father & the Son:

if I go and prepare a place for you, I will come back and take you to be with me that you also may be where I am.  (14:3)

 in the Father-Son relationship of leader-follower:

I am in my Father, and you are in me, and I am in you. Whoever has my commands and keeps them is the one who loves me. The one who loves me will be loved by my Father, and I too will love them and show myself to them (14:20f). I love the Father and do exactly what my Father has commanded me (14:31).

in the love of the Father-Son relationship (and notice how love and obedience go together):

As the Father has loved me, so have I loved you. Now remain in my love. If you keep my commands, you will remain in my love, just as I have kept my Father’s commands and remain in his love.  (15:9f)

in the joy of the Son:

I have told you this so that my joy may be in you and that your joy may be complete. (15:11)

in the knowledge that the Son has of the Father:

You are my friends if you do what I command. I no longer call you servants, because a servant does not know his master’s business. Instead, I have called you friends, for everything that I learned from my Father I have made known to you.  (15:14f)

and even in the opposition from the world:

“If the world hates you, keep in mind that it hated me first. If you belonged to the world, it would love you as its own. As it is, you do not belong to the world, but I have chosen you out of the world. That is why the world hates you. Remember what I told you: ‘A servant is not greater than his master.’ If they persecuted me, they will persecute you also. If they obeyed my teaching, they will obey yours also. They will treat you this way because of my name, for they do not know the one who sent me. If I had not come and spoken to them, they would not be guilty of sin; but now they have no excuse for their sin. Whoever hates me hates my Father as well. If I had not done among them the works no one else did, they would not be guilty of sin. As it is, they have seen, and yet they have hated both me and my Father. (15:18-24).

in the generosity of the Father:

In that day you will no longer ask me anything. Very truly I tell you, my Father will give you whatever you ask in my name. Until now you have not asked for anything in my name. Ask and you will receive, and your joy will be complete. “Though I have been speaking figuratively, a time is coming when I will no longer use this kind of language but will tell you plainly about my Father. In that day you will ask in my name. I am not saying that I will ask the Father on your behalf. No, the Father himself loves you because you have loved me and have believed that I came from God. (16:24-27)

There's much more in these chapters, but this idea of sharing in the relationship of the Father & the Son isn't just in John 13-17 . Think of how Paul speaks of our being 'in Christ', 'seated in the heavenly realms', 'adopted as sons of God', united in Christ etc., in different ways all of these contain an echo of Christ's relationship with his Father - a relationship which we now have the glory of sharing!
And one application of this: we tend to think of Christian service as a burdensome command. But surely to love as Christ loved and serve as he served is not a burden but a wonderful, glorious privilege! If we could really understand and believe this, wouldn't it transform our attitude towards serving God's people, the church, and towards loving non-Christians in the way Christ loved us while we were still sinners?