What does Paul mean when he prays, “that Christ may dwell in your hearts through faith” (Ephesians 3:17)? He is not praying for unbelievers, but for the saints at Ephesus. Why pray for believers that Christ may dwell in their hearts? The definition of a believer is that the Spirit of Christ dwells in him (Romans 8:9). How can you pray that someone who is already in your heart dwell in your heart?
I suggest that it means: “Lord, keep on dwelling in their hearts and don’t forsake them.” Even if you believe in the eternal security of the elect (which I do), that does not rule out praying for their perseverance. The elect are secure precisely because they persevere. And perseverance is certain because it is the promise and work of God (Romans 8:30; 1 Peter 1:5). And this work of God is performed in answer to prayer (Luke 22:32; 1 Thessalonians 5:23–25). Therefore it is possible to believe in eternal security and also to pray earnestly that Christ would keep dwelling in a person’s heart. These very prayers are ordained of God for the perseverance which leads to salvation (Philippians 1:19).
If this is what Paul means (may Christ keep on dwelling in you!) then the little phrase “through faith” becomes mighty important. His prayer is that Christ may dwell in your hearts through faith. That means that, if you want Christ to be with you, you must depend on him. You will know the reality of Christ’s presence in you if you are leaning on him. If you sit on your horse, it is under you. If you get off and walk, it is not. How shall we have Christ always within us?
Ride on him! “Christ never yet forsook in need, the soul that trusted him indeed.” Don’t wait for some consciousness of Christ’s presence before you trust. He is there “through trust.” Christ is present when he is trusted. He will be ridden or he will vanish. If you sit on your horse, it is under you. If you don’t, it is not.
Paul said in Galatians 2:20, “It is no longer I who live, but Christ who lives in me. And the life I now live in the flesh I live by faith in the Son of God.” “I don’t live, but Christ lives in me” corresponds to “I do live by faith.” This must mean that living by faith and having Christ live in me are the same thing. Which is another way of saying Christ dwells in our heart through faith. Or: If you sit on your horse, it’s under you.