that Christ will dwell in your hearts through faith, so that, because you have been rooted and grounded in love,
The prayer is directed at the Father. Not at Jesus or at the Holy Spirit. Not as if Jesus and the Holy Spirit are not God, but if you want a prayer protocol, this is it. It is a prayer to the Father.
We are asking the Father to do something, but whatever that thing is, it will involve the Spirit and the Son, as we see in the prayer Paul began in verse 16.
He prayed that God would do something to their inner person through His Spirit (Ephesians 3:16), and in the same breath, as we see in this verse, he asks that Christ would dwell in their hearts through faith.
So we see his prayer focused on our inner person, on our hearts. In short, Paul is praying for spiritual advancement. And in his view, only God can grant it.
It's a prayer for spiritual growth by another name. He is praying for a robust spiritual life centered on Christ, faith, and love, with a focus on our hearts.
Christ
Only the message of Christ is true spiritual food, and He is the word of God (John 1:1), and Peter said we should desire the sincere milk of the word that we would grow (1 Peter 2:2).
Faith
Faith is the prioritization of what is unseen as opposed to what is seen, in the hope of heaven, in the hope of eternal life. We see Noah as an example of faith (Hebrews 11:7). He obeyed in the present for a future reward.
Love
There are so many alternative things that we are grounded in that run our lives; these are things we can call idols, other allegiances we may know we have, things and people we are devoted to and need, the sun in our lives that we gravitate towards, that our hearts constantly tilt towards in anger. complaint and fear, rather than to God and loving Him.
Do not love the world or the things in the world. If anyone loves the world, the love of the Father is not in him, because all that is in the world (the desire of the flesh and the desire of the eyes and the arrogance produced by material possessions) is not from the Father, but is from the world. And the world is passing away with all its desires, but the person who does the will of God remains forever.
That was the same John who wrote, "Beware of idols” (1 John 5:21), who wrote about not loving the world or the things in the world. That covers the alternative loves we can have. Jesus, on his own, warned about serving/loving money (Matthew 6:24). Maybe that is a stand-in for the world, especially when you juxtapose that with Paul saying that the love of money is the root of all evils (1 Timothy 6:10)?
So when Paul prayed that we should be rooted and grounded in love, it is not without cause, in my opinion.
Heart
When Jesus was asked about the greatest commandment, he said, “Love the Lord your God with all your heart, with all your soul, and with all your mind” (Matthew 22:37).” It starts with the heart, which we can define as the seat of affection, or fondness, or affinity, or attachment.
But if there is a place that is inaccessible to man, it is his heart. He can climb the mountain to get to the top, fly to the moon to pick up a rock, and peer into the stars to discover light in far-flung galaxies, but the heart is a mystery.
But God, seeing the heart, makes him an effective, unquestioned judge. We don't need to look further than the book of Jeremiah to read about the heart condition of man.
The human mind is more deceitful than anything else.
It is incurably bad. Who can understand it?
So if something controls your heart, it controls your life. Praying that Christ will dwell in your heart through faith connects three things. It’s what determines what you are magnetized to. And if it is not fully founded on the love of God, that is a very dangerous place to be, hence the temptation we have a proclivity for.
Let no one say when he is tempted, “I am tempted by God,” for God cannot be tempted by evil, and he himself tempts no one. But each one is tempted when he is lured and enticed by his own desires. Then when desire conceives, it gives birth to sin, and when sin is full grown, it gives birth to death. Do not be led astray, my dear brothers and sisters.
In summary: Christ as the animating principle reshaping the hardware of your life into his image, founded on the love of God; faith as the electric supply that makes everything work.
What we are talking about is a heart reshaped and transformed, anchored in faith as a constant reality of the life of the believer. As it is written, the just shall live by faith (Romans 1:17).
And there is the need to be rooted and grounded in love.
Again, there are amazing dimensions to this prayer, all about what we are focused on, who we are being transformed into, and this is about our inner person and heart, not so much about a list of dos and don'ts. Paul is not coming with a top-down list, but with prayer. He cannot presume to know the mind of God for each person, but God does, so he turns to prayer. I pray that we would likewise turn to prayer rather than speculate.
And Paul telling Christians that Christ should dwell in our hearts when we are Christians is about identification with Christ, about being formed into Christ.
And Paul will expand on that later in this book when he says we need to grow into Christ (Ephesians 4:15).
But practicing the truth in love, we will in all things grow up into Christ, who is the head.
The point is: the journey is not over.