There are many passages that refute the Reformed Protestant belief that, at initial justification, not just one's past and then-present sins, but also one's then-future sins are remitted (e.g., 1 John 2:1-2; Heb 2:17; 6:4-6; 10:26-29). Another potent passage that refutes this heresy is 2 Pet 1:9:
For anyone who lacks these things is nearsighted and blind, and is forgetful of the cleansing of past sins.
Here, Peter speaks of believers who are lacking godliness, brotherly kindness, and charity (v.7), and speaks of their having, in their ignorance and return to sin, of their past sins having been remitted. This is rather baffling if the Reformed view is true, and these individuals who are under condemnation from Peter received a blanket forgiveness of their sins, not just past but also future; indeed, the Greek clearly speaks only of past sins having been remitted: τῶν πάλαι αὐτοῦ ἁμαρτιῶν ("their past sins"). This is inconsistent with Reformed soteriology.
Interestingly, the verse also speaks of their sins having been "cleansed" (Gk.: καθαρισμος); as BDAG informs us, this is a verb used to describe the cleansing one receives during a cultic ritual:
cleansing from cultic impurity, purification (2 Macc 2:16 of the dedication of a temple) J 3:25. W. subj. gen. κ. τῶν Ἰουδαίων 2:6. W. obj. gen. of the pers.: Mk 1:44; Lk 5:14 (Manetho in Jos., C. Ap. 1, 282 deals with the ceremonies that a person who has been healed of leprosy undergoes). αἱ ἡμέραι τ. καθαρισμοῦ αὐτῶν (cp. Ex 29:36) Lk 2:22 includes Joseph in the purification, whereas only the woman was required to undergo purification (Aristot., HA 7, 10 p, 587b, 1ff this is called καθαρμός); the pronoun αὐτῶν perh. is colloq. usage to account for Joseph’s presence in the process.
Indeed, many commentators understand this to refer to the salutary effects of water baptism:
The Greek phrase translated as “forgetful of the cleansing of past sins” reads literally as “receiving forgetfulness” (lethen labon). It as though forgetfulness of the ethical force of baptism overtakes people, with the result that the virtuous life abandons them. (Lewis R. Donelson, I & II Peter and Jude [New Testament Library; Louisville, Ky.: Westminster/John Knox Press, 2010], 222)
This is another passage that (1) supports LDS theology and (2) refutes Reformed theology. Yet again, “Biblical Christianity” is to be found within The Church of Jesus Christ of Latter-day Saints.