We’ve all had the experience of trying to tell another person something important — and realizing that they’re not really listening. Their body may be present but their mind is elsewhere. Or they’ve actually heard what you said, but for one reason or another refuse to accept it.

And if we’re being honest with ourselves (you’re reading this in private, right?), we’ve been that person, the one who refused to listen to something we probably needed to hear.

The prophet Isaiah knew about this. In the temple, he was given a vision of God’s glory and became terrified that he would be stricken down for his sins — specifically, he wailed that he was a man of “unclean lips” (Isa 6:5, NRSV). But one of God’s seraphs (think, high-ranking angel) flew to Isaiah and purified his lips with a burning coal, preparing him to be a spokesperson for God.

Here’s what Isaiah was told to say:

‘Keep listening, but do not comprehend;
keep looking, but do not understand.’
Make the mind of this people dull,
    and stop their ears,
    and shut their eyes,
so that they may not look with their eyes,
    and listen with their ears,
and comprehend with their minds,
    and turn and be healed.

Isa 6:9b-10

The message seems harsh. Does God not want his rebellious people to repent, to come back, to be reconciled, to be healed?

Yes, of course he does.

But here we confront a brutal reality of our fallen human nature — what the Bible describes as “hardness of heart.” Simply put: if we’ve already mistakenly made up our minds about something, being confronted with the truth won’t make us say, “Oh, really? I had no idea. I guess I was wrong.” Instead, we stubbornly dig in our heels, plug our ears, and refuse to listen.

This reality can make the prophet’s vocation a lonely one. On one side is a vision of God and God’s unshakeable truth; on the other is the stubborn rejection of the prophet and his message.

Isaiah wasn’t the only one who had that experience.

The Synoptic Gospels (Matthew, Mark, and Luke) all record Jesus’ parable of the sower — or perhaps more accurately, the parable of the soils (Matt 13:3-9; Mark 4:2-9; Luke 8:4-8). Whether the prophecy of Isaiah or Jesus’ message of the kingdom, God’s word is like a seed. It may fall upon fertile soil, sprout, and grow. But it may also fall where there is no soil or only shallow soil and never put down good roots. It may also fall in a place where any growth will be choked by surrounding weeds.

When Jesus tells this parable, his disciples ask what it means and why he speaks in such riddles to begin with. In response, he tells them that they are privileged to have the inside track, “to know the secrets of the kingdom of heaven” (Matt 13:11; cf. also 13:16-17). But regarding everyone else, he quotes the words given to Isaiah (cf. Matt 13:14-15; Mark 4:12; Luke 8:10) — the people may listen, but they won’t understand.

In the gospel of John, Jesus does not quote Isaiah 6. But John himself does.

The context is the final week of Jesus’ earthly ministry, after his Triumphal Entry into Jerusalem. John observes, as he has throughout his gospel, that the people in general still did not believe in Jesus, despite the many miracles he had performed in their presence, miracles that John typically describes as “signs” that should have pointed them to God and the coming of God’s king and kingdom. But no: they could not believe because their hearts were hard, and John quotes Isaiah 6 to make sense of that tragic rejection (John 12:40).

Clearly, the words given to Isaiah are foundational to the vocational vision of those who would speak for God in any age. No matter how clearly or truthfully one might present the gospel, not everyone will respond in a positive way. Isaiah knew it. Jesus knew it. Matthew, Mark, Luke, and John knew it.

And, as we’ll see, Paul knew it as well.