John Lightfoot on Matthew 3:15

[Thus it becomes us to fulfil all righteousness.] That is, 'that we fulfil every thing that is just.' Now in the baptism of Christ there were these two just things especially:--I. That this great priest, being initiated into his ministerial office, should answer the type of the admission of the Levitical priests, who were initiated by washing and anointing; so was he by baptism, and the Holy Ghost. II. When, by the institution of Christ, those that entered into the profession of the gospel were to be introduced by baptism, it was just, yea, necessary, that Christ, being to enter into the same profession, and to preach it too, should be admitted by baptism.