This is a good question. This is a question that many pastors get on a regular basis, or at least I know I do. While I am sure there are many different loving, truth-filled ways to respond to this concern, here is one option:
Hey Mike! Thanks so much for sharing with me. I can totally relate to what you are saying, as I am sure most, if not all, Christians can, if they are honest. I know I have had seasons in my walk with the Lord where my head was full of truth about God and the Gospel, but my heart felt cold, joyless, even numb at times. And I hated it. I hated the "disconnect," as you put it. So be encouraged and know you are not alone in this.
When we are feeling this way, it is hard to make sense of passages that instruct us to DELIGHT and REJOICE in the Lord from the heart and not just the head, such as:
Deut 6:4 You shall love the Lord your God with all your heart and with all your might.
Psalm 37:4 Delight yourself in the Lord.
Psalm 42:1-2 As the deer pants for the water, so longs my soul after thee, O Lord.
The reality is that sometimes (perhaps many times) we must fight for our joy in the Lord. We have to fight to be grateful for the Gospel. That might sound like a strange way of saying it, but I really believe it is true. Pastor and author John Piper has helped me a ton with this in my own life. He says, "The preservation of our joy in God takes work. It is a fight. Our adversary the devil prowls around like a roaring lion, and he has an insatiable appetite to destroy one thing: the joy of faith. But the Holy Spirit has given us a sword called the Word of God for the defense of our joy" (John Piper, Desiring God, 123).
I believe he is right. In fact this is a daily fight for joy in God as we seek to grow closer to Jesus and allow the Word of God to transform our hearts and minds from the inside out. It takes time. It does not happen overnight like we wish it would. But it happens. This is part of our progressive sanctification into the likeness and image of God. Clearly, if God commands us to delight and rejoice and take pleasure in Himself, then He will also provide the power to carry these commands out in our hearts so that we can fulfill them. Joy in the Lord, delight in the truths of God, gratefulness for the Gospel; these are not only possible, this is what God longs to do in your heart and mine as His children. He desires that both our head and our heart would overflow with the truth and joy of the Lord!
Ok, so let me throw some resources your way that I think could really help you in your fight for joy in the Lord right now. I know these have helped me a great deal.
1. First of all, John Piper's book, "When I Don't Desire God: How to Fight for Joy" is a book I come back to over and over again. God has used this in huge ways in this struggle in my own life over the years and I know it has done the same for many others.
Here is the link to the book (you will notice that an online copy of it is free....also, if you want my copy I would love to give it to you, seriously...just let me know): http://www.desiringgod.org/resource-library/books/when-i-dont-desire-god
2. Here is the link to a seminar Piper gave on the book that you can watch or listen to: http://www.desiringgod.org/resource-library/conference-messages/by-conference/2005-regional-conference
3. Here is the link to a great article on developing a theology of the heart as well as the head by Dr. Ray Ortlund. Good stuff here: http://www.monergism.com/thethreshold/articles/onsite/pleasures.html
Let me close by giving you a list of 15 ways to fight for joy in God in your life. This list has been adapted from a similar list on desiringgod.org. You may want to use these in your time alone with God this week. Spend time looking up the Scriptures, praying, and meditating on these truths, asking the Holy Spirit to help you grow in these areas of your walk with Him:
1. Realize that authentic joy in God is a gift (Galatians 5:22-23)
2. Realize that joy must be fought for relentlessly (1 Timothy 6:12, 2 Corinthians 1:24)
3. Resolve to attack all known sin in your life (Romans 8:13)
4. Learn the secret of gutsy guilt - how to fight like a justified sinner (Micah 7:8-9) (I'd better explain this one: it means that we feel guilty about our sin, but we don't collapse because of it. We know that we are in a secure position because of the cross.)
5. Realize that the battle is primarily a fight to see God for who he is (Psalm 34:8, 2 Corinthians 4:4-6, 2 Corinthians 3:18)
6. Meditate on the Word of God day and night (Psalm 19:8, Jeremiah 15:16, John 15:11, Psalm 1:1-3)
7. Pray earnestly and continually for open heart eyes and an inclination for God (John 16:24, Psalm 90:14, Psalm 85:6, Psalm 51:12, Psalm 119:36, Psalm 119:16, Psalm 90:40)
8. Learn to preach to yourself rather than listening to yourself (conquer your thoughts, tell yourself what to think...fill your mind with truth! - Psalm 42:5)
9. Spend time with God-saturated people who help you see God and fight the fight (1 Samuel 23:16, Hebrews 3:12-13, Proverbs 13:20)
10. Be patient in the night of God's seeming absence (Psalm 40:1-3)
11. Get the rest, exercise, and proper diet that your body was designed by God to have (stop trying to prove you're God by staying up to get things done - go get some sleep!!! Psalm 127:1-2)
12. Make a proper use of God's revelation in nature (Psalm 19:1)
13. Read great books about God and biographies of great saints (I can recommend many to you if you want)
14. Do the hard and loving thing for the sake of others (Isaiah 58:10-11)
15. Get a global vision for the cause of Christ and pour yourself into the unreached (Psalm 67:1-2)
Ultimately, I pray you will find rest and peace and joy in the Gospel of grace! You are loved by the Father unconditionally through Jesus. This is not based on anything you do or don't do but is entirely based on what Christ has achieved on your behalf through his life, death, and resurrection! You are LOVED! You are a beloved, adopted son of the most high God. This will never change. I pray this truth brings you comfort and yes, a little joy.
Know that I am praying for you as we fight this good fight together. And thanks for sharing your struggle with me. This is why myself, along with our other pastor-elders, are here. It is our joy to walk with you and encourage you on this journey.
Thankful for you, my friend.
For your joy in Him,