The cedars and oaks represent the tall and massive and strong and majestic trees of nature.
The mountains and hills represent the powerful and awe inspiring vastness and security of making oneself hidden.
Now the towers and fortified walls represent manmade and mans efforts in early detection and defensive structures.
Towers are places of observation. Constructed high on fortress or city walls, they offered a view of the surrounding area such that an enemy or messenger or anyone traveling by, could be seen from a distance.
Fenced or fortified walls, were usually built thick and tall, in order to prevent an enemy from breaching the defenses and getting into the fortress or city being defended.
Throughout history man has constructed higher and higher walls, and better and better defensive structures, but in every case, none have served to prevent an enemy from overcoming the defenses.
Man is impressed with the natural majesty and strength of nature. Man is impressed with the work of his own hands. Man is impressed with his own self.
And yet, none of these things will stand before God when the day and hour come for the final judgment of man and history.\
There is nothing in this world and nothing in your life that can hide you, that can exempt you, that can prevent Gods judgment from overtaking you.
Without God, even this world will crush you. The world cannot prevent itself from destruction.
Therefore, if you choose indifference toward God, toward doctrine, then you have no defense. There is no alternative for your protection. There is nothing in this world, nothing in your imagination, nothing in your ingenuity that can save you from what is coming in your life. Indifference includes defining your own way.
Just as you could not prevent the day of your birth, and you cannot prevent the day of your death, so too, your life is totally in Gods hands, not yours. All you can do is choose a side for God or against, and then reap the rewards or curses that will apply.