"저는 선생님으로 취직해요."
Translation:I get a job as a teacher.
In English, it is necessary. Some languages will omit the indefinite article for statements of occupation, but English is not one of them.
Sometimes you can omit the indefinite article for job position/title, but it indicates specificity and usually the name of the position. Acceptable: "I just got a job as Director of Marketing" or "I got a job as Director of Marketing at Example Corp." Unacceptable: "I got a job as teacher." Acceptable: "I got a job as Head Teacher."