He accepts them because...
Apparition #2 came in the form of a blood child which told him not to fear the power of man because no child born of a woman would defeat him. He agrees with this because he believes that he can't be defeated by anyone and this apparition simply helps justify his thoughts.
Apparition #3 came in the form of a child with a crown holding a tree which told him not to fear those who hate him or conspire against him, because he shall not be defeated until the battle of Birnam Wood on Dunsinane Hill, and he doesn't even believe he would be defeated so the second part didn't even register in his mind.
