There are three parts to this statement:
a - "God is ABLE to deliver us from the blazing furnace"
b - "God WILL deliver us from our hand"
a' - "but even if He does not, we will not bow"
If we think that b & c go together, this seems confusing, but actually, a & a' are meant to go together to form one statement: "God is able to deliver us from the furnace, but even if He chooses not to, we will not bow" (this is called a chiasm)
this is a two-part statement of faith. They are expressing faith in God's power and trust in his wisdom of how to exercise that power.