"Despair and faith," as expressed in the Abrahamic traditions correspond fairly closely to "nihilism and eternalism" in the Mahayana tradition, with the key difference that both are considered extreme views to be avoided with all due diligence in the Buddhist tradition.
Actually, I would differ with your parallel on these. As I understand them from Buddhist tradition, nihilism would hold that the self is ultimately eliminated and of no enduring reality and thus karmic action has no "real" reference to it. This is usually illustrated in the life of Gautama Buddha by his early hedonism and embracing of all attachments. "Nothing matters anyway, so..."
Eternalism would hold that the self (small "s") is eternal and therefore karma is not active on anything but its transient aspects, hence karmic action is equally transient and not of "real" consequence. This is usually illustrated in the ascetic period of Gautama Buddha's life, where he attempted to deny all attachments in search of the eternal.
True doctrine would hold instead that the Tathagata is real beyond attachmane or non attachment, (Nagarjuna's Middle Way), apart from all appearances or non-appearances, and is neither eternal in arising or not arising, nor contingent in its existence or non-existence. It is beyond all affirmation or denial. It simply Is: Thus.
Karma and sin are clearly related doctrines, but with different perspectives on the contingent nature of self and reality, and its operative risks of awareness and intention, illustrated by your comment. The dangers of nihilism and eternalism in Buddhism are a loss of awareness of what is Absolute and real, and thus both are paths to obscuring illusions (maya).
The Abrahamic faiths posit a fallen nature in need of redeeming and inherently unworthy of it. We call this nature "sin." "Despair" in this setting leads to the destruction of life, either from the processes of hedonistic exhaustion, brutalizing sadism or the erotic surrender to extinction (love of death). This is something all too evident in recent events.
"Faith" in contrast leads to life's fulfillment -- "that you may have life in more abundance." Love, the greatest commandment, gives rise to faith; and faith gives rise to hope. Hope leads from death into life.
The inverse process is that the realization of the transient nature of things leads to despair, and despair leads to despite, and despite leads to extinction -- from life into death.
The difference is that where Buddhism posits a problem of cyclical dialectic to resolve successive aspects of perceived duality (or sudden global synthesis), Christianity particularly, and the Abrahamic faiths, generall,y posit a process of linear, historically contingent physical and moral development conditioned by physical and moral entropy, with the ever-present possibility of a non-linear and non-contingent interruption not conditioned by that process, or any process.
I find these two perspectives non-dual.