There are vital principles here for us, and we must not forget that the subject is still sowing the seed, witnessing for Christ, preaching the message of salvation. The first point is: take heed what you hear.
While salvation is entirely free, unearned – there is nothing we can do to contribute to it; it is entirely by grace through faith – yet once we are Christians, subsequent blessing from the Lord is conditional. It is then different. Salvation is free, but ongoing assurance and blessedness is conditional. Conditional upon what? On our obedience to the Lord, and, in this context, on our readiness to make him known, because we value so highly the message of the gospel.
But more generally, if you hear this message casually, without humility, without valuing God’s word as supremely precious, then you will receive nothing from it. How you hear, determines what you receive. If you have no respect for this message, and you are not humbled by it, you are not concerned that it should affect your life, then you will not receive more light from God. What you receive depends on how you hear.