'A sandal tree' signifies aspects of the natural self.

(References: Apocalypse Explained 518)

301. Verses 2, 3. And I saw a strong angel proclaiming with a great voice, Who is worthy to open the book, and to loose the seals thereof? And no one in heaven, neither upon the earth, nor under the earth, was able to open the book, or to look thereon.

"And I saw a strong angel proclaiming with a great voice," signifies influx of the Lord into heaven: "Who is worthy to open the book, and to loose the seals thereof?" signifies, whether any one there is of such a quality as to know and perceive the states of the life of all.

"And no one in heaven, neither upon the earth, nor under the earth, was able to open the book, or to look thereon," signifies, manifestation, that no one knows and perceives, of himself, anything of the state of the life of all in general and of each in particular.