Romans 10:16

But they have not all obeyed the gospel. For Esaias saith, Lord, who hath believed our report?

Not all who hear gospel preaching obey it, and this fulfills Isaiah's lament asking who has believed the report. Faith arrives through hearing, and such hearing arrives through the word of God. Yet the word preached brings no profit to hearers unless it is mixed with faith in those who hear it.

The saving response is that with the heart a person believes unto righteousness, with the mouth confession is made unto salvation, and everyone who calls on the name of the Lord will be saved. By contrast, hearers leavened with evil surmising shut the word out of their hearts and receive no blessing from what they hear. They do this by talking carelessly about the message, criticizing the messengers, and pointing out defects in the message, instead of receiving it into good and honest hearts.