Kim,
The language of conditional and unconditional is imo somewhat misleading. The real emphasis is upon who takes the oath. So in the Sinitic (Mosaic) covenant, the people take the oath as the redeemed vassal. They must uphold the stipulations to fulfill the oath. The problem is that since the Fall original sin precludes this as a possibility. Thus the sacrificial system is enacted to make provision for this weakness. This is all well in good for those external sins (i.e. those touching ritual purity in Leviticus 1-15). The Day of Atonement makes provision for these external sins. However, those of the conscience or dealing with inner conformity of the Law Leviticus 17-25 have no provision for forgiveness in the Mosaic Law, hence they merit the curses of Lev 26.
Now in the Noaic, Abrahamic, Davidic, and New Covenants, God takes the oath to fulfill the requirements and provisions for these covenants. Hence why in Matthew 1:1, Christ Jesus is set forth as the true seed of Abraham and David. Here we see that Jesus in coming to fulfill the
pactum salutis (inter-Trinitarian covenant of which the Covenant of Grace is dependent), he triumphs over sin, death, and Satan and is given the elect as his inheritance (cf. Psa 2).
So the issue is not conditional/unconditional but the emphasis is rather on who takes the oath in a covenant. We can extrapolate from them that the Noaic, Abrahamic, Davidic, and New covenants are settled and unshakable by human faithlessness, because God is trustworthy and true and will accomplish what he has sworn. The Mosaic covenant relies upon human faithfulness to obtain the blessings. Since humans are frail and week post-fall this covenant is unsure and those who made the oath and relied upon it for salvation will ever always meet the "sword of the vengeance of the covenant" (see Hebrews 4-8).
I would highly recommend
Michael Horton's God of Promise for a more detailed explanation.