Isaiah uses the symbolism of comparing the Lord to a young mature lion that stands over his prey, protecting that which belongs to him, and not intimidated by shepherds, or even large numbers of shepherds, regardless of the weapons they bring, until finally the shepherds disperse and go away or are chased away, being intimidated themselves.
Zion, throughout the Bible, is represented as the dwelling place of God. God is truth, and lives in truth, and therefore, Zion, represents the body of truth or Bible doctrine, which is the possession of God.
Believers in Christ, are the possession of God. And therefore God, will stand guard over, and fight for, all believers, who are His family, and possession.
The point of this verse, is to demonstrate to the people of Judah in Isaiah’s day, and to all believers throughout history, that it is better to put their trust in Christ, than it is to enter into an alliance with Egypt, which represents sin.
Jesus Christ, using this comparison, would be no more alarmed at the number and power of enemies, than a lion, that is determined to stand over and hold his prey.
And of course you would probably have to come face to face with the power and authority and intimidation of a lion, in order to really understand and appreciate this comparison.
Most people, if they came face-to-face with a determined lion, would quickly realize that they are no match for the lion.
Likewise, all enemies of God are no match for God.
Therefore, it is far better to look to God in times of need, than it is to look to the things of this world.