“Thus says the Lord: ‘What wrong did your fathers find in me that they went far from me, and went after worthlessness, and became worthless?'” (ESV – Read the chapter)
When someone rejects God, there’s a reason for it. That seems like it should be obvious, but perhaps it’s not so obvious as it should be. If someone has been exposed to the Gospel and then left it for something else, there’s a reason for it.
That’s what God is challenging the Israelites on here. Why did they leave Him in pursuit of something else? Did they find something else more attractive? Were they dissatisfied with God? Why did they leave? Why did they pursue something with no enduring worth? Didn’t they know we become like what we worship? Didn’t they know that in pursuing something empty of value they would find themselves becoming empty of value as well?
When we are sharing the Gospel with someone who has heard it before, we need to keep in mind the fact that they didn’t accept it the first time for a reason. If we don’t try and take into account what that reason was or is, we are likely going to be wasting our time (and theirs).
Increasingly in our culture, sharing the Gospel will more and more come to involve apologetics. We will need to be able to make good arguments and defend why we are convinced that what we believe is more reasonable and likely-to-be-true than what they believe. Part of these apologetic efforts will necessarily involve learning more about what they believe in order to be able to meaningfully show why it is a less reasonable position to hold than our own.
And, of course, all of this will have to be paired with a life that is its own positive apologetic for the worthwhileness of the Gospel. It will come most often out of the context of a relationship, but where that is not the case, it will come because we have invested time to learn about other common worldviews in order that we will be able to be prepared to offer counter arguments no matter what they profess to believe. We are entering a world in which sharing the Gospel will neither look nor work like it has in the past. Yet our charge has not changed and so we must adapt.