The real question should be Can you be too heavenly minded to be of any earthly good?
Usually when someone says this about another believer they refer to the person's zeal for God. Perhaps this person constantly talks about God, maybe they always have their nose in the Bible, perhaps they are always shouting God's praises, always trying to tell everyone that God loves them. Maybe they volunteer constantly at church or they always want to pray for others.
But is this a bad thing? Personally, I don't think anyone can be too heavenly-minded to be of any earthy good. In fact, I'll go a step further and say that the more heavenly-minded we are, the more earthly good we will be!
Was Jesus too heavenly minded? Doesn't He fit the description above? Was He of any earthly value? I'd say He was the most valuable person who ever walked the earth!
But you might say, can't someone be so passionate for God that they turn others off? Absolutely!. Jesus turned a lot of people off. Many people hated him. Does that make what He did or who He was any less important or valuable? And aren't we supposed to follow in His footsteps?
Yet, I think some people shy away from becoming too zealous for God. They believe in Jesus, love Him, but they don't want to act like one of those "religious nuts" . They use this phrase about being too heavenly minded as a excuse for their complacent Christianity. After all, they don't want to turn people away! They want to draw them in!
But I say to them, how you can draw people in to something you don't have? In truth, it has been my experience that the closer I become to God, the more a part of my every thought and action He becomes, the more people are drawn to me. Why? Because the world is looking for something real. They are tired of fake ads and fake claims and broken promises. If God is real, they want to see His life operating through His followers. Otherwise, the joy salvation peace and purpose He offers is just another empty claim.
Will people reject you? Make fun of you? (Even some Christians) Absolutely! But you're in good company!
I should probably end this here but I have one more thing to add. I do believe that a person can be too religiously minded to be any earthly good. These are the pharisee types who instead of telling others about God's love, they tell them about their sin. How they shouldn't be doing this and they shouldn't live like that, etc. I believe those kind of people do the most damage of all.
Let's strive not to be religiously minded but to be Christ-minded! Let's strive to be zealous in our faith, to speak of, to think of, to breathe in God every minute. And then watch who He will send your way.