Jesus used the image of sheep to represent His followers because this symbol embodies qualities of meekness, obedience, and unconditional trust in their Shepherd.

The Shepherd’s Flock: Embracing Humility and Salvation

Jesus used the image of sheep to represent His followers because this symbol embodies qualities of meekness, obedience, and unconditional trust in their Shepherd. Sheep—an animal not associated with perfection or high status in the world, but instead seen as an embodiment of humility and vulnerability. That is why Christ, calling Himself the Good Shepherd, emphasized that true salvation and the path to eternal life are open to those who, like sheep, know how to listen to His voice and follow Him.

As stated in one of the sources:
"But He is not only the door, He is the Shepherd. He led His sheep out of the old enclosure of Moses' law and calls them to Himself; they follow Him, and He, as the Good Shepherd, guides them to the bliss of eternal life..." (source: link txt).

It is also noted that the sheep was not previously exalted or idealized in the eyes of people, and its meekness was even considered a weakness:
"But nowhere in the world was a sheep deified, nowhere was it elevated to an ideal. Sheep's meekness was regarded as weakness and even a vice. Christ did something unheard of and unseen—He transformed a menagerie into an enclosure for sheep..." (source: link txt).

Thus, the choice of sheep as a metaphor for describing His followers underscores the idea that the salvation and the new order established by Christ are intended for ordinary, humble people who sincerely follow the voice of their Savior. This image also helps to break down the established notion that only members of a certain elite or narrow circle can be chosen, showing that the true Kingdom of God is a united, mixed flock under the leadership of the one Shepherd (source: link txt).

Supporting citation(s):
"But He is not only the door, He is the Shepherd. He led His sheep out of the old enclosure of Moses' law and calls them to Himself; they follow Him, and He, as the Good Shepherd, guides them to the bliss of eternal life..." (source: link txt)
"But nowhere in the world was a sheep deified, nowhere was it elevated to an ideal. Sheep's meekness was regarded as weakness and even a vice. Christ did something unheard of and unseen—He transformed a menagerie into an enclosure for sheep..." (source: link txt)
"But Christ did not come solely to lead the Jews out of the enclosure of Moses' law and into the Kingdom of God; He came to save the whole world... and thus one mixed flock will be formed under the leadership of one Shepherd—Christ." (source: link txt)