It would seem that the four Gospels are ‘carefully crafted and culturally contextualized catechetical documents.’

Matthew seems to be explicitly catechetical, in that he arranges his material according to subject matter rather than chronological sequence.  The result is a handbook on the words and deeds of the Church’s founder.

Mark is often found, in our own day, to provide an excellent basis for catechetical courses such as Christianity Explored.

Luke (along with Acts) was written, in the first place, to provide initial or follow-up catechesis for Theophilus.

As for John, ‘the absence of any direct account of Jesus’s baptism, transfiguration, and institution of the Lord’s Supper, which might undergird the profound Trinitarian teachings on the new birth and the Bread of Life that John records so fully, would seem to support the time-honored guess that John was intentionally writing a higher catechetical supplement to initial Christian instruction, such as the Synoptic Gospels provide.’

Based on, and quoting from, Packer and Parrett, Grounded in the Gospel: Growing Believers the Old-Fashioned Way.