The concept of the "word" descending from heaven comes from Deut 30:11-14, which is quoted by the Apostle Paul in his epistle to the Romans.
Romans 10:5-11 (NASB)
5 For Moses writes that the man who practices the righteousness which is based on law shall live by that righteousness. 6 But the righteousness based on faith speaks as follows: “Do not say in your heart, ‘Who will ascend into heaven?’ (that is, to bring Christ down), 7 or ‘Who will descend into the abyss?’ (that is, to bring Christ up from the dead).” 8 But what does it say? “The word is near you, in your mouth and in your heart”—that is, the word of faith which we are preaching, 9 that if you confess with your mouth Jesus as Lord, and believe in your heart that God raised Him from the dead, you will be saved; 10 for with the heart a person believes, resulting in righteousness, and with the mouth he confesses, resulting in salvation. 11 For the Scripture says, “Whoever believes in Him will not be disappointed.”
Paul is applying "Christ" as the referent in the Deuteronomy passage. In other words, the "Christ" is the Son of David (ref. Davidic Covenant). The covenant was comprised of "words" from God spoken as promises to David, which resonated with eternal implications. When we turn to the Book of Deuteronomy, we also see the additional correlation of bread; that is, God's word is equated with the manna from heaven. In other words, God's words are living bread upon which man lives --
Deut 8:2-3 (NASB)
2 You shall remember all the way which the Lord your God has led you in the wilderness these forty years, that He might humble you, testing you, to know what was in your heart, whether you would keep His commandments or not. 3 He humbled you and let you be hungry, and fed you with manna which you did not know, nor did your fathers know, that He might make you understand that man does not live by bread alone, but man lives by everything that proceeds out of the mouth of the Lord.
The source of the bread was God's word. The manna was therefore dependent on the Lord's command (that is, His word articulated), and thus the word of God was "bread" in the ultimate sense (otherwise the manna would have never appeared without the commandment given by the Lord in heaven). No commandment from God's mouth, no bread; ergo, man lives by every word that proceeds from the mouth of God. In summary, those "words" are divine revelation as captured in Scripture.
The flesh and blood of Christ also fit into this same picture. That is, he is the "lamb of God" (Jn 1:29 and Jn 1:36), and therefore he is the sacrifice, which occurred on the Passover.
1 Corinthians 5:7 (NASB)
7 Clean out the old leaven so that you may be a new lump, just as you are in fact unleavened. For Christ our Passover also has been sacrificed.
The reference to the Feast of Unleavened Bread is in view in which the Passover occurred. In other words, Paul is saying that Jesus Christ was the Passover Lamb, which was eaten on the Passover. Please click here (schematic) or here (conceptual) for the alignment of the Passover with the sacrifice of the Lamb of God.
So we "eat" this lamb, who is the "bread" from heaven. We therefore "ingest" him when we believe on the Word of God (i.e., we "take in" the bread that comes down from heaven). When we drink his blood, we receive eternal life. We see this in the next verse (noted below), which is the only place in the Christian New Testament where the blood includes water, which removes the contamination of death. That is, the Hebrew Bible is specific that "blood is life" (Gen 9:4; Lev 17:11; Lev 17:14; Deut 12:23; and Deut 19:6), but what we now find in the Christian New Testament is that the blood of Christ not only includes his mortal life, but his eternal life as well.
Hebrews 9:18-20 (NASB)
18 Therefore even the first covenant was not inaugurated without blood. 19 For when every commandment had been spoken by Moses to all the people according to the Law, he took the blood of the calves and the goats, with water and scarlet wool and hyssop, and sprinkled both the book itself and all the people, 20 saying, “This is the blood of the covenant which God commanded you.”
Neither in the Masoretic Text nor the Septuagint does the Hebrew Bible in general and the Book of Exodus in particular (Exod 24:8) ever mention ANYTHING concerning the sprinkling of water as part of "the blood of the covenant." (Please note the "water, scarlet wool, and hyssop" describe the particular water mentioned in Numbers 19:1-22; another parallel is found in Leviticus 14:4-8, however, there the blood is sprinkled, but cleansing is consummated by washing of water.) That is, the author of the Book of Hebrews includes the sprinkled water as inclusive of "This is the blood of the covenant which God commanded you." In the both passages just noted, the water (that was filtered through the ashes of the Heifer and/or under the sacrifice of an animal in a container) was sprinkled to "wash away" contamination with dead people or animals, or, in the case of leprosy, to "wash away" the contamination of dying flesh. So the author of the Book of Hebrews is saying that the "blood of the covenant" not only included the animal's red bodily fluid, but also water (filtered through ashes and/or poured beneath sacrificed animals), which removed contamination of death or leprosy, which was decomposing dying flesh. So the "blood" includes not only mortal life but eternal life as well. In other words, in the Hebrew Bible the water pointed to the eternal life of Christ in the New Covenant (described further below), which was what "washed away" the contamination of death (via resurrection); the "blood" of the New Covenant was this eternal life (further discussed below).
So to "eat" the meat of the Paschal Lamb was to ingest the "bread" from heaven -- the Word of God. To drink his blood is not to drink the red liquid substance that circulates inside the body, which was very very very abhorrent to the Christian New Testament Jewish mind (Acts 15:20; Acts 15:29; and Acts 21:25), but to drink the living water, which is the eternal life of Jesus Christ. Jesus referred to this eternal life as "living water" (Jn 4:10).
So, in summary, to believe on him is to "eat" him (in the same way the Paschal Lamb was eaten at Passover, which enabled one to escape the bondage of "Egypt"), and to drink his blood, which means to ingest his eternal life. That is, "the iron furnace" was Egypt (Deut 4:20; 1 Ki 8:51; and Jer 11:4); the blood is what set the prisoners free from the waterless pit (please see Zechariah 9:11).
Remember, Jesus introduced the cup of the Lord's Table as the "blood of the New Covenant" (Luke 22:20). In the context of the New Covenant in the Hebrew Bible, the liquid mentioned is NOT "blood" (red substance that circulates inside the body), but is instead "WATER" (please compare Ezek 36:24-26 with Ezek 37:21-23, where the New Covenant "cleansing" is with water).
In other words, Jesus is saying that his "blood" includes his eternal life, which saves us from the waterless pit ("iron furnace") of sin and death. Please refer again to the parallel of the sacrifice of Jesus Christ with the Passover.
In closing, when we understand the "blood of Christ" to include his eternal life, we can infer that when he stated that he was thirsty on the cross (John 19:28), he was not only implying that his mouth was dry, but also that he was dead on the cross spiritually (even though he was yet still alive mortally), since he lacked "living" water. That is, eternal life died on the cross through the person of Jesus Christ, but because eternal life was "indestructible" (Acts 2:24 and Hebrews 7:16), he conquered and therefore "washed away" death. Thus while his body was the sacrifice for the sins of the entire world (compare 2 Cor 5:21 with 1 Jn 2:2), this sacrifice would have been in vain were eternal life unable to conquer death (1 Cor 15:17-19). Thus the "blood" of his mortal life and the "blood" of his eternal life worked in tandem not only to atone for sins, but to save unto eternal life.
One more closing statement: the so-called "sacraments" do not save - please click here for Paul's discussion from the Hebrew Bible that "sacraments" have no intrinsic salvific value. While the Lord's Table represents his death on the cross (eating flesh and drinking blood), and water baptism represents receiving eternal life (washing away spiritual death), participation in the sacraments provide no intrinsic salvific value when understood through the "plain and normal" interpretation of the Word of God.