Matt 28:19 is a "proof-text" for the Trinity (see this page for a LDS response to this). For those who may be curious, here is an excerpt from a book defending Modalism that addresses it (in case anyone wanted to know how a modalist would approach this verse):
.
. . it may be asked, Why a plurality of names at all? Why not say, Baptize in
the name of God? To which I respond, Why not say, Believe in Christ? Christ
does say, He that believeth on the Son (Jo. vi: 40), and Paul does speak of
“him which believeth in Jesus” (Rom. iii: 26): why need Peter leap into a wider
formula? and why does he say so carefully, “Believe in the Lord Jesus Christ,
and thou shalt be saved, and thy house?” (Acts xvi: 31).
In
fact, why does it say “name”? Why does it not say names? If Father, Son
and Holy Ghost are hypostatically different, they may be the same in substance,
and yet difference of Persons would eminently discredit the singular, “name.”
Our blessed Lord was God and man. As “Lord,” he was the Greek for Jehovah; as
“Jesus” he was Jehovah a Saviour; as Christ, he was an Anointed Man. In either
of the three appellatives, there was a distinct idea; but who says that
believing in the Lord Jesus Christ is anything but believing in the one
Emmanuel?
3.
But it will be said; and this is by far the strongest consideration,--The Son is
different; and, therefore, the same may be argued in respect to the Spirit. No
man imagines Jesus to be different from Christ; but men do imagine the Father
to be different from the Son. The Son is weak (Heb. v: 2). The Son prays (Lk.
xxii: 44). The Son is man (Mar. vi: 3). The Son dies (Matt. xxvii: 50); and
does what the Father could do. Whatever may be said of the Spirit, no one
denies that the Father is different from the Son: and why then, in the
Baptismal Formula, do we not have a like discrepance imagined for the Spirit. (John
Miller, Is God a Trinity? [3d ed.; Princeton, N.J.: Self-published,
1922], 127-28, italics in the original)