Leviticus 19:26

You shall not eat the flesh of any sacrifice while the blood remaineth in the veins. You shall not be observers of auguries, after the sanhedrin of the speculators.

Do not eat on blood This commandment (which prohibits eating meat from any of the permitted species of animals until its blood is dashed upon the Altar of God) logically follows the previous one (which prohibits eating fruit from a domesticated tree until the fifth year). It applies only in the vicinity of the Sanctuary, and this is borne out by Sha ul’s words [I Samuel 14:34], for he had the Ark with him [I Samuel 14:18]. By saying [I Samuel 14:33] that they were “eating on blood”, it is as if Scripture accused them of eating sacrifices to the satyrs. As I have explained, it was an Egyptian custom to offer sacrifices to demons; and if one has not dashed the blood against the Altar in the name of God, it is apparent that one is eating in the name of demons. For this reason the commandment is juxtaposed to Do not believe in omens: The Egyptians used to eat on blood, and stray after the demons; the Canaanites used to believe in omens, and in propitious times (as it is written [Deuteronomy 18:14]). Once again Scripture associates Egyptian and Canaanite practices, as expressed earlier by “the deeds of the land of Egypt…the deeds of the land of Canaan” [18:3]. People look for omens to test things about which they are uncertain, as in “I have tested you by divination, and have established that God has blessed me…” [Genesis 30:27]. Shapes, special rods, unusual events, and arbitrary movements have all been used as omens, as well as days of the year or hours of the day.

Do not believe in auspicious times [Hebrew: lo t‘onenu] Some people say that this word comes from “answer” [Hebrew: ‘ana]: one concentrates on some particular question, and listens carefully to something to hear how he will be answered. This etymology is grammatically unacceptable. Other people relate the word to “her scheduled times” [Hebrew: ‘onatah] [Exodus 21:10]. In my opinion the word derives from “cloud” [Hebrew: ‘anan]. It is well known that people perform divination on clouds, by observing their shapes and their movements. The word is most likely an ‘ayin- ‘ayin verb (as in “to turn” [Hebrew: s-b-b]). Here the verb is in the polel form. It appears in the qal form in “soothsayers like the Philistines” [Isaiah 2:6]. A clearer example is found in “a diviner of auspicious times, or a diviner of omens” [Deuteronomy 18:10].

YE SHALL NOT EAT WITH THE BLOOD. “This passage has been explained in many different ways in Tractate Sanhedrin.” This is the language of Rashi. Now the conclusion of that discussion in the Talmud is that all those interpretations [of the verse before us] are Torah-ordained, since Scripture included all manner of “eating with the blood” in one negative commandment. And if so, that which Scripture states in the case of Saul, Behold, the people sin against the Eternal, in that they eat with the blood, means that they transgressed one of the prohibitions included in this negative commandment, since they were eating of an animal [slaughtered properly] before its life had entirely left it. It is with reference to this that Scripture states there, And the people flew upon the spoil,, Verse 32. like a bird of prey that tears its victim and eats it, and they took sheep, and oxen, and calves, and slew them on the ground; and the people did eat them with the blood., Verse 32. Because of the abundance of spoil of cattle [that they had taken from the Philistines], as soon as [they were slaughtered properly and] their blood was spilled on the ground, they tore off their limbs and ate them before life had entirely left the animals.
In line with the plain meaning of Scripture, this seems to have been a kind of witchcraft or divination, since [the meaning of this passage] may be deduced from its context; [i.e., from the second half of this verse which states, neither shall ye practice divination nor soothsaying, we may deduce that the first half of the verse, Ye shall not eat with the blood also refers to some form of witchcraft, as will be explained]. Thus they used to spill the blood [of the cattle] and gather it in a hollow, which was then attended, according to their opinion, by the satyrs, and they would eat at their tables to tell them future events. Now when the Israelites were at that time camping with Saul, they were very much afraid of the Philistines, and Saul did nothing except for inquiring of the Urim and Thummim, as it is said, Let us draw near hither unto G-d, while the people were inquiring of the satyrs or of witchcraft to know their way and what to do, and they were eating with the blood in order to perform that craft [mentioned above]. It is for this reason that Scripture there states, Then they told Saul, saying: ‘Behold, the people sin against the Eternal, in that they eat with the blood.’ And he said: ‘Ye have dealt treacherously,’, Verse 33. meaning to say: “Behold, G-d has wrought for you this day this great salvation, and you inquire of no-gods! It is treachery!” I will yet explain the prohibition against soothsaying and enchanting.

לא תאכלו על הדם, according to the plain meaning of the text this is something we can derive by merely reading the context in which it has been written, i.e. while the blood of the slaughtered animal has not yet been removed.

לא תנחשו ולא תעוננו, unless warned against these practices the Jews would also engage in such practices as eating on the grave of the slain for the sake of protecting themselves against the vengeance by the spirit of the murdered person (particularly murdered witches). The Talmud Sanhedrin 63 lists a number of possible scenarios described by our verse.

לא תאכלו על הדם לא תנחשו ולא תעננו, all of these practices were commonplace also among the Israelites who were desperate to gain advance knowledge of what was in store for them individually. Such practices had to be eradicated if the people were to progress from an overall environment of spiritual morass, רוח טומאה, to spiritual bliss, רוח טהרה ונבואה, spiritual purity and prophetic spirit.