Which is not, strictly speaking, grammatically correct) is likely the reason you're having trouble with this.
Thank you TD for magnificently pointing this out. People in general have not realized this nuance.
With all my respect to you, We at JW understand more than you figure:
Abstain from doing what? When a doctor tells you to abstain from alcohol, he means consuming ethanol. In a funny way though, he is telling you to stay away from alcohol; it’s that serious. Is pumping a gallon of ethyl alcohol into your veins “keep abstaining?” I think it is ironic that God chose a physician to write this decree and at the end of his letter although it is only a greeting -but him being a doctor and all-he writes: “Good Health to You” as if keep abstaining from alcohol for medical reasons is implied in the greeting. Strictly not going beyond what is written though, new gentile Christian were to -as you point out-abstain from blood as the Jews had been abstaining from blood. It is noteworthy that although It wasn’t realized or understood at the time, some of God’s laws to Israel were for medical reasons including dietary laws so how can you factor out medical purpose from dietary in “keep abstaining? “ It is also interesting that WT latest commentary points out that the laws on blood in the Mosaic covenant did not apply to non-Jews although the Noachide laws are still binding upon all of humanity, seeing that wt cites Leviticus in support of JW stance. Also, at the time of this epistle, the Mosaic law was abolished and Jews were not legally required to observe the laws on blood as stipulated in the law covenant. So what could this decree actually have meant by keep abstaining since the law covenant was abolished, was is more than Noachide to both Jews and Christians? Were now all Christians to participate in that part of the covenant dealing with blood meaning that the decree now binds it upon both Jews and Christians? WT commentary references Leviticus explaining that although the law covenant applied only to Israel (and keep in mind that when the epistle was written the Mosaic law did not apply) God’s view in the law pertaining to blood was serious, involving the death penalty. So in keep abstaining relating to this scripture, God also views it as very serious when you violate his law on blood in modern times. Cofty’s commentary mitigates this by equating that consuming blood drawn from a living host is the same to God as the blood from an animal that died naturally because in both cases no life was taken. However, “keep”ing with how Jews abstained from blood in the past and the noachide, there is no scriptural basis in not abstaining from blood in new ways of consuming blood.
By the way, cofty’s argument is very interesting and his article is worth reading in my humble estimate.