Isaiah had an extremely hard task. He had to preach to people who would not believe. More - he had to preach judgement and destruction on the surrounding nations. This was his calling.
How did he go about that task? He did so with tears. Isaiah preached out of a sensitive heart, a heart that wept over overs. We see this in Isaiah 15v5: "My heart cries out over Moab..." Also in 16v9: "So I weep, as Jazer weeps, for the vines of Sibmah. Heshbon and Elealeh, I drench you with tears!" And again in 16v11: "My heart laments for Moab like a harp, my inmost being for Kir Hareseth." In these verses we see Isaiah's heart. Isaiah was no hard-hearted preacher. He proclaimed God's message with feeling.
Actually Isaiah's heart was a reflection of God's heart over the lost. Our God is not willing that any should perish and pleads with people to "turn to him and be saved." Jesus, God's Son, showed this heart during his life and ministry. He wept over Jerusalem and the judgement that was coming.
Preachers who spend time with Jesus become like him.