“If you believe that Christ death on the cross forgave all future sins, then you do not understand the Bible and reject Christ’s teachings.”
Roman’s 8:28-39 clearly rejects this premise.
28 And we know that for those who love God all things work together for good, for those who are called according to his purpose.
29 For those whom he foreknew he also predestined to be conformed to the image of his Son, in order that he might be the firstborn among many brothers.
30 And those whom he predestined he also called, and those whom he called he also justified, and those whom he justified he also glorified.
31¶ What then shall we say to these things? If God is for us, who can be against us?
32 He who did not spare his own Son but gave him up for us all, how will he not also with him graciously give us all things?
33 Who shall bring any charge against God’s elect? It is God who justifies.
34 Who is to condemn? Christ Jesus is the one who died—more than that, who was raised—who is at the right hand of God, who indeed is interceding for us.
35 Who shall separate us from the love of Christ? Shall tribulation, or distress, or persecution, or famine, or nakedness, or danger, or sword?
36 As it is written, “For your sake we are being killed all the day long; we are regarded as sheep to be slaughtered.”
37¶ No, in all these things we are more than conquerors through him who loved us.
38 For I am sure that neither death nor life, nor angels nor rulers, nor things present nor things to come, nor powers,
39 nor height nor depth, nor anything else in all creation, will be able to separate us from the love of God in Christ Jesus our Lord.
One can quote scripture, but not fully understand it or explain it.
Paul states that none of the outside forces can not destroy our relationship with God, but that we can. (Rom 2;5-10) and Rom 6:16) and Rom 8:13 and Rom 11:21
I tell you, on the day of judgment men will render account for every careless word they utter; for by your words you will be justified, and by your words you will be condemned (Matt. 12:36-37).
Anyone that believes all future sins were forgiven because Christ died on the cross for all future sins is gravely mistaken and is endangering their salvation.