John Gill Commentary Luke 4:43

"But he said unto them, I must preach the good tidings of the kingdom of God to the other cities also: for therefore was I sent." — Luke 4:43 (ASV)

And he said to them
In answer to their importunate requests:

I must preach the kingdom of God to other cities also ;
as well as to Capernaum; and though they did not express their desire of his continuance with them, in order to preach the Gospel to them; yet Christ signifies that a principal part of his work lay in preaching the things concerning the kingdom of God, the Gospel dispensation on earth, the doctrines and ordinances of it, as well as the things which relate to the kingdom of glory; as what is the saints meetness for it, their regeneration, and their right to it, which lies in his righteousness:

And that as he had preached these things at Capernaum, there was a necessity upon him to preach them in other cities of Galilee and Judea: for therefore am I sent; as he was by his heavenly Father, and had himself also undertook and engaged to do it.