It's not a "metaphor" for anything. It is what it says it is: the blood that was shed on the Cross from the flesh of the God-Man.
Baptism effects the work of the Blood, yes, but we wouldn't say it's a "symbol" of the Blood.
I think the difference you're referring to stems from the misuse by some western Christians of these verses. The blood of Jesus is seen exclusively as a divine and infinitely worthy forensic and legal transaction paid by the Son to the Father in order to "square our bill" with the Father, thus "justifying" and "cleansing" us from our sin, which is ultimately a legal debt in the mind of the Father that needs to be cleared.
We definitely use the blood of Jesus, but our use of it tends to be much more ontological and based on our obedience, which I would say is the use we see in those passages you cited. Mankind, as St. Athanasius pointed out, owed a debt, but it was not a debt of offense or transgression of law to the Father, but rather a natural consequence of mortality that was the direct result of our separating ourselves from the Source of our life. We are brought from the body of death we're in and placed in a place where we can potentially "serve the living God." We, then, "if we walk in the light, as he is in the light," make use of the Life that is in the Blood which then counteracts the death in our members.
for a more lengthy reflection of mine.