Every person admitted to practice as an attorney and counsellor at law shall, before his name is entered upon the roll to be kept as hereinafter provided, take and subscribe an oath, substantially in the following form:
     I do solemnly swear (or affirm, as the case may be), that I will support the constitution of the United States and the constitution of the state of Illinois, and that I will faithfully discharge the duties of the office of attorney and counselor at law to the best of my ability.