In verse 18 there is a break from the main storyline as John provides background information about the Jews' disbelief. (See: [[rc://en/ta/man/translate/writing-background]])
# he does not keep the Sabbath
This means Jesus does not obey the law about doing no work on the Jewish Day of Rest.
# How can a man who is a sinner do such signs?
This remark appears in the form of a question to emphasize that Jesus' signs prove he is not a sinner. AT: "A sinner can not do such signs!" (See: [[rc://en/ta/man/translate/figs-rquestion]])
# signs
This is another word for miracles. "Signs" give evidence that God is the all-powerful one who has complete authority over the universe.
Here "Jews" is a synecdoche for the "Jewish leaders" who opposed Jesus. AT: Now the Jewish leaders still did not believe. (See: [[rc://en/ta/man/translate/figs-synecdoche]])