On receiving his call, Isaiah was immediately aware of his shortcomings. God dealt with these and Isaiah responded willingly, even though he was warned that the people would be hard-hearted and not accept his message. God withdraws His Spirit from some, so that they are hardened; others, He softens.
Like Isaiah, Christ was also sent with a ministry of grace and reconciliation, but also of judgment. When His disciples asked Him why He spoke in parables, He answered by quoting from this passage in Isaiah.
We learn that we must witness to all people, whatever their reaction may be and that we must be careful not to harden our hearts when God’s Word tells us something we might not want to hear.