Back before Bluetooth, the remote controls for our TVs used infrared light to shine their signals to the TV, telling it to power on, change channels, or mute the commercials. The remote had a little light bulb on the end that emitted this signal, but the light that came out was infrared light, part of the spectrum that's invisible to the naked eye. So no matter how long or how hard you pushed, it looked like a dead bulb.
When I worked at Radio Shack, we sold these little cards - about the size of a business card - which had a yellow strip across the front. These cards were for testing remote controls. When you pointed an infrared remote at this strip, the invisible light that bounced off it became visible. Even though the bulb itself still seemed to not be working, when you pointed it at the card, the light could be seen.
This is what the Holy Spirit does for Christians, in our hearts, when we hear or read the Word of God. For some people, reading the Bible is like trying to see the light of an infrared remote: it just sounds like confusing, meaningless, dead words. There was a time in my life when this is what it was like for me. But one day the Holy Spirit stepped in and suddenly those words lit up inside of me! After so long hearing and feeling nothing, I was suddenly filled with knowledge and power and wonder.
When we have the opportunity to share God's truth with the people in our lives, we must understand that sometimes those words will be like infrared light, producing no effect in our listeners' hearts. But we must faithfully share them anyway because we never know which day will be the day that the Holy Spirit causes them to become visible. Today a friend told me how according to his Muslim beliefs, he needs to work hard at being good and will still have to spend some time in hell when he dies as punishment for his sins. I took the opportunity to share with him that in Christ, my sins are already paid for, and that I do good deeds because I'm saved, not in order to be saved. To me this sounded like the most beautiful news, but my words did not yet light up his heart.
What a relief it is to know that even if we don't see the effect of our words, that we've done our part. God will decide when and where those words will illuminate. It's up to us to just faithfully point our remotes at people (share the good news), even if people tell us that they don't see the light (it still sounds like foolishness). Oh, how sad it would be to not share God's light on the day the Lord is ready to make it visible to them! "...preach the word; be ready in season and out of season..." (2 Tim 4:2)