What is the Best explanation for the Trinity?

The best explanation for the Trinity is one short sentence about God.

1 John 4:8 (NKJV)

He who does not love does not know God, for God is love.

Read that slowly, because John is not saying that God is affectionate, or that God is in a good mood towards us. He says love is what God is.

Now think about what love is. Love is never a solitary thing. It always involves someone doing the loving and someone being loved. So a sentence like “God is love” is telling us something about God before He made anything at all.

In the upper room, hours before He was arrested, Jesus prayed out loud, and John wrote down what He said. The whole of John 17 is one person of the Trinity speaking to another, and we are permitted to listen.

John 17:5 (NKJV)

And now, O Father, glorify Me together with Yourself, with the glory which I had with You before the world was.

Notice that Jesus is clearly addressing the Father, and recalls the relationship He shared with Him before the world existed. A few sentences later He says:

John 17:24 (NKJV)

Father, I desire that they also whom You gave Me may be with Me where I am, that they may behold My glory which You have given Me; for You loved Me before the foundation of the world.

You loved Me before the foundation of the world. Before Adam, before the mountains, before there was a single created thing to love, love existed within the Godhead. The Holy Spirit is not standing outside this. Scripture calls Him both the Spirit of God and the Spirit of Christ (Romans 8:9), and He is the one who pours the Father's love into the hearts of His people (Romans 5:5). He belongs to the same eternal life of the one God.

This also corrects a mistake people make constantly. Many assume God created the world because He was lonely, or because He wanted somebody to love. That would mean something was missing in God until we turned up. Nothing was missing. Paul told the philosophers in Athens that God is not served by human hands as though He needed anything (Acts 17:25). The life of God was full before there was a universe. He made the world freely, as a gift, not to obtain something He lacked. Your existence is not God meeting a need of His own; it is God giving.

1 John 4:10 (NKJV)

In this is love, not that we loved God, but that He loved us and sent His Son to be the propitiation for our sins.

Not that we loved God. The movement starts at His end, not ours. And His love is not drawn out of Him by anything He finds impressive in us. God said exactly that to Israel when He explained why He had chosen them.

Deuteronomy 7:7–8 (NKJV)

The LORD did not set His love on you nor choose you because you were more in number than any other people, for you were the least of all peoples; but because the LORD loves you, and because He would keep the oath which He swore to your fathers, the LORD has brought you out with a mighty hand, and redeemed you from the house of bondage, from the hand of Pharaoh king of Egypt.

Read the reason God gives: because He loves you. There is nothing behind it in you. His love never began as a reaction to something you did.

So the best explanation of the Trinity is not a diagram showing how one can be three. It is an answer to a question nobody thinks to ask: what was God doing before He made anything? He was loving. The Father loved the Son, the Son loved the Father, and the Spirit shared that same life. Christians do not hold this doctrine because they are fond of puzzles. They hold it because it is the only way the sentence “God is love” can be true of God Himself, and not merely of God once He had us.