Unitarianism is a belief that diminishes Christ to a lesser being, among other things. Seventh-day Adventists do not believe in Unitarianism. Seventh-day Adventists believe in a Godhead consisting of three equal Persons, who are one in nature, character and purpose {PP 34.1}
Yes! As Paul stated, "1 Corinthians 5:7 "Purge out therefore the old leaven, that ye may be a new lump, as ye are unleavened. For even Christ our passover is sacrificed for us:" (Read more on this important subject by clicking on this link.)