You don't seem to understand that the gnostic's being fought against were those who denied The Eucharistic Real Presence and things like the Divinity of Christ
Just take a look at what Saint Irenaues writes,dear sister..
"So then, if the mixed cup and the manufactured bread receive the Word of God and become the Eucharist, that is to say, the Blood and Body of Christ, which fortify and build up the substance of our flesh, how can these people claim that the flesh is incapable of receiving God's gift of eternal life, when it is nourished by Christ's Blood and Body and is His member? As the blessed apostle says in his letter to the Ephesians, 'For we are members of His Body, of His flesh and of His bones' (Eph. 5:30). He is not talking about some kind of 'spiritual' and 'invisible' man, 'for a spirit does not have flesh an bones' (Lk. 24:39). No, he is talking of the organism possessed by a real human being, composed of flesh and nerves and bones. It is this which is nourished by the cup which is His Blood, and is fortified by the bread which is His Body. The stem of the vine takes root in the earth and eventually bears fruit, and 'the grain of wheat falls into the earth' (Jn. 12:24), dissolves, rises again, multiplied by the all-containing Spirit of God, and finally after skilled processing, is put to human use. These two then receive the Word of God and become the Eucharist, which is the Body and Blood of Christ." -"Five Books on the Unmasking and Refutation of the Falsely
Named Gnosis". Book 5:2, 2-3, circa 180 A.D. "For just as the bread which comes from the earth, having received the invocation of God, is no longer ordinary bread, but the Eucharist, consisting of two realities, earthly and heavenly, so our bodies, having received the Eucharist, are no longer corruptible, because they have the hope of the resurrection." -"Five Books on the Unmasking and Refutation of the Falsely named Gnosis". Book 4:18 4-5, circa 180 A.D.
FWIW, I'm not impressed with William Webster at all- It's pretty easy to prove him wrong by even using other protestants such as J.N.D Kelly who were far more knowledgeable than Webster on the Church Fathers
Here is some of what Kelly wrote..
http://www.catholic.com/tracts/the-real-presence
Renowned Protestant historian of the early Church J. N. D. Kelly, writes: "Eucharistic teaching, it should be understood at the outset, was in general unquestioningly realist, i.e., the consecrated bread and wine were taken to be, and were treated and designated as, the Savior’s body and blood" (Early Christian Doctrines, 440).
From the Church’s early days, the Fathers referred to Christ’s presence in the Eucharist. Kelly writes: "Ignatius roundly declares that . . . [t]he bread is the flesh of Jesus, the cup his blood. Clearly he intends this realism to be taken strictly, for he makes it the basis of his argument against the Docetists’ denial of the reality of Christ’s body. . . . Irenaeus teaches that the bread and wine are really the Lord’s body and blood. His witness is, indeed, all the more impressive because he produces it quite incidentally while refuting the Gnostic and Docetic rejection of the Lord’s real humanity" (ibid., 197–98).
"Hippolytus speaks of ‘the body and the blood’ through which the Church is saved, and Tertullian regularly describes the bread as ‘the Lord’s body.’ The converted pagan, he remarks, ‘feeds on the richness of the Lord’s body, that is, on the Eucharist.’ The realism of his theology comes to light in the argument, based on the intimate relation of body and soul, that just as in baptism the body is washed with water so that the soul may be cleansed, so in the Eucharist ‘the flesh feeds upon Christ’s body and blood so that the soul may be filled with God.’ Clearly his assumption is that the Savior’s body and blood are as real as the baptismal water. Cyprian’s attitude is similar. Lapsed Christians who claim communion without doing penance, he declares, ‘do violence to his body and blood, a sin more heinous against the Lord with their hands and mouths than when they denied him.’ Later he expatiates on the terrifying consequences of profaning the sacrament, and the stories he tells confirm that he took the Real Presence literally" (ibid., 211–12).
On the contrary, I DO understand what the Gnostics believed and the main issue the ECFs disputed with them about was that Jesus, God incarnate, was flesh and blood. They used the facts that bread and wine symbolized the real flesh and blood of Christ to demonstrate His reality. The doctrine of transubstantiation - which took many centuries to develop - is a close cousin to Gnostic theology because both claim that "things are not what they appear". The very definition of Transubstantiation is that the "elements" remain under the appearance of bread and wine, but are miraculously changed by the prayer of consecration into the actual body and blood of Christ. That alone should show that this would be totally in line with what Gnosticism taught because they believed that Jesus did not have flesh and blood but only "appeared" that way. As it was, at that time both the Orthodox and Gnostic view was in the symbolic nature of the Eucharist. The difference was that the Gnostics refused the physical Jesus existed. Irenaeus said:
"How can they (Gnostics) be consistent with themselves when they say the bread for which they give thanks is the body of their Lord and the cup his blood, if they do not say he is the Son of the Creator of the world? ... Let them either change their views or avoid offering the bread and wine. But our view is in harmony with the eucharist, and the eucharist confirms our view".(Irenaeus, Against Heresies IV.xviii.4, 5)
Tertullian also said: "Taking bread and distributing it to his disciples he made it his own body by saying, "This is my body," that is a "figure of my body." On the other hand, there would not have been a figure unless there was a true body." (Tertullian, Against Marcion IV. 40)
But, as I have explained before, the larger problem with teaching the elements become the flesh and blood of Christ is the associated teaching that the Eucharist is sacrificial and salvific. Jesus taught that believing in Him was receiving Him. To believe on Him is eating His flesh and drinking His blood because that is what saves. The incorrect view, IMO, is to teach that one MUST regularly receive these elements in the Mass in order to be infused with partial grace.
Rather than teach what Jesus did that those who believe on Him HAVE eternal life and the observance of the Last Supper communal service was for "remembrance of me", the Catholic AND Orthodox Churches insist that faith is not enough to ensure eternal life in Heaven with God. To require "works", either refraining from sin, obedience to the "commandments of Christ", participation in the "sacraments", prayer, giving or every other good deed in order to merit everlasting life flies in the face of the very meaning of "grace". We are not saved according to our works, but by grace through faith. Assembling with other believers and participating in the breaking of bread - the Communion/Lord's Supper - is identifying with Christ. It is an outward sign of an inward reality of having already received Christ as Savior. When Paul speak of partaking in an "unworthy manner", I know there are many different version of what he meant but I think at least one of those meanings would be someone who participates in the observance, eats the bread offered and drinks the wine, but who has not accepted Christ as Savior. That must come before the observance just as baptism should come after one has received Christ.
I know we may not agree on the doctrine, but I appreciate your kind reply. God bless you as you seek to always walk with him.