accomplishments than Macbeth but greater in spirit and character.

"Not so happy, yet much happier" doesn't make much sense, because Banquo is going to be murdered by Macbeth.

Perhaps Banquo is happy to know that his descendants will rule Scotland, including James VI of Scotland—who became James I of England, for whom Shakespeare likely wrote Macbeth, and who believed that he was descended from Banquo. (He wasn't, but he liked to believe he was.)

In act 4, scene 1, Macbeth receives warnings and prophecies from the apparitions, or the visions that Macbeth experiences in the witches' cave.

The first apparition that appears to Macbeth is "an Armed Head," presumably a head with a helmet on it.

FIRST APPARITION. ... Beware
Macduff;
Beware the Thane of Fife. (4.1.79-80)

Macbeth appreciates the warning, but Macbeth is no fool, and he's well aware that Macduff is a threat to him.

MACBETH. Whate'er thou art, for thy good caution, thanks;
Thou hast harp'd my fear aright. (4.1.81-82)

The second apparition, "a bloody child," appears.

SECOND APPARITION. Be bloody, bold, and resolute; laugh to scorn
The power of man, for none of woman born
Shall harm Macbeth. (4.1.87-90)

This prophecy isn't absolute, like "All hail, Macbeth, that shalt be King hereafter!" (1.3.50-53). What's unspoken in this prophecy is that there's a possibility that Macbeth will encounter such a man. This prophecy is conditional. Macbeth has nothing to fear unless or until he meets a man who was "none of woman born," which he does.

The third apparition is "a Child Crowned, with a tree in his hand."

THIRD APPARITION. ... Macbeth shall never vanquish’d be until
Great Birnam Wood to high Dunsinane Hill
Shall come against him. (4.1.103-105)

The important word in this prophecy is "until." This prophecy isn't at all conditional. It's a certainty. Birnam Wood is going to come to Dunsinane.

Macbeth is oblivious the true meaning of the prophecy—because he believes that the Second Apparition told him that he's invincible—and he also fails to recognize the visual clue here: the child holds "a tree in his hand."

Macbeth visualizes the entire Birnam forest rising up and marching on Dunsinane castle. He doesn't envision Birnam Wood marching on Dunsinane branch by branch or tree by tree, which is exactly what happens.

There is a fourth and even more disturbing vision.

Macbeth's insists on an answer to his question, "shall Banquo's issue ever / Reign in this kingdom?" (4.1.114-115)

The cauldron sinks into the stage, there's a sudden, loud sound of oboes, and "a show of eight Kings, and Banquo last with a glass in his hand" appears to Macbeth. The apparition shows a long line of kings, all descendants of Banquo, and it shows Banquo "with a glass in his hand"—a mirror that reflects an infinite succession of Banquo's descendants as kings.

Macbeth fails to realize that the prophecy that's revealed in this fourth apparition encompasses all of the other prophecies. This apparition foretells that Banquo's issue is going to reign in Scotland, and for a long, long time. This means that Birnam Wood is coming to Dunsinane, and Macbeth will be vanquished, and that Macbeth will encounter a man "not of woman born," and he will be harmed by that man.

Macbeth asks a final, fateful question:

MACBETH. ... What, is this so? (4.1.137)

The answer:

FIRST WITCH. Ay, sir, all this is so. (4.1.138)

The witch's answer is wholly unambiguous and unequivocal. "All this is so." All of these things will happen.

Macbeth sees what he wants to see, however, and hears what he wants to hear, and he leaves the cave believing that he's invincible.

He's very wrong about that.