We do not celebrate Christmas or other religious festivals throughout the calendar year as holy feasts established by God. The only period in time Adventists celebrate as holy is the weekly Sabbath (from Friday sunset to Saturday sunset).
Kanisa does find, however, that these holidays provide good occasions to focus on the Christian aspects, that is, the biblical message of the death and resurrection of Jesus (at Easter), and of His incarnation and coming to earth as a human being (at Christmas). It also gives valuable opportunities to speak with other people about the gospel. Also, these events are often occasions for building family fellowship and reaching out to the poor and needy.