book 23:The trunk of the olive tree.: Explain the symbol of the olive tree's trunk. Why is it so important to the story???

There was the bole of an olive tree with long leaves growing strongly in the courtyard, and it was thick, like a column. I laid down my chamber around this … Then I cut away the foliage of the long-leaved olive, and trimmed the trunk from the roots up, planning it with a brazen adze, well and expertly, and trued it straight to a chalkline, making a bedpost of it, and bored all hones with an auger.

The bed symbolizes the marriage of Penelope and Odysseus, it is immovable...... completely secure, just like their marriage.