"breaking one and the same bread, which is the medicine of immortality, and the antidote to prevent us from dying, but [which causes] that we should live for ever in Jesus Christ."
Eph. 5:2 μηδεὶς πλανάσθω· ἐὰν μή τις ᾖ ἐντὸς τοῦ θυσιαστηρίου, ὑστερεῖται τοῦ ἄρτου τοῦ θεοῦ.  εἰ γὰρ ἑνὸς καὶ δευτέρου προσευχὴ τοσαύτην ἰσχὺν ἔχει, πόσῳ μᾶλλον ἥ τε τοῦ ἐπισκόπου καὶ πάσης τῆς ἐκκλησίας.
Eph. 5:2 Let no one be misled: if anyone is not within the sanctuary, he lacks the bread of God. For if the prayer of one or two has such power, how much more that of the bishop together with the whole church!
Eph. 20:2 μάλιστα ἐὰν ὁ κύριός μοι ἀποκαλύψῃ «τι»  οἱ κατ᾿ ἄνδρα κοινῇ πάντες ἐν χάριτι ἐξ ὀνόματος συνέρχεσθε ἐν μιᾷ πίστει καὶ ἑνὶ  Ἰησοῦ Χριστῷ, τῷ κατὰ σάρκα ἐκ γένους Δαυίδ, τῷ υἱῷ ἀνθρώπου καὶ υἱῷ θεοῦ, εἰς τὸ ὑπακούειν ὑμᾶς τῷ ἐπισκόπῳ καὶ τῷ πρεσβυτερίῳ ἀπερισπάστῳ διανοίᾳ, ἕνα ἄρτον κλῶντες, ὅ  ἐστιν φάρμακον ἀθανασίας, ἀντίδοτος τοῦ μὴ ἀποθανεῖν ἀλλὰ ζῆν ἐν Ἰησοῦ Χριστῷ διὰ παντός.
Eph. 20:2 especially if the Lord reveals anything to me. Continue to gather together, each and every one of you, collectively and individually by name, in grace, in one faith and one Jesus Christ, who physically was a descendent of David, who is Son of man and Son of God, in order that you may obey the bishop and the presbytery with an undisturbed mind, breaking one bread, which is the medicine of immortality, the antidote we take in order not to die but to live forever in Jesus Christ.
Rom. 4:1 Ἐγὼ γράφω πάσαις ταῖς ἐκκλησίαις καὶ ἐντέλλομαι πᾶσιν ὅτι ἐγὼ  ἑκὼν ὑπὲρ θεοῦ ἀποθνήσκω, ἐάνπερ ὑμεῖς μὴ κωλύσητε. παρακαλῶ ὑμᾶς, μὴ εὔνοια ἄκαιρος γένησθέ μοι. ἄφετέ με θηρίων εἶναι βοράν,  δι᾿ ὧν ἔνεστιν  θεοῦ ἐπιτυχεῖν. σῖτός εἰμι θεοῦ, καὶ δι᾿ ὀδόντων θηρίων ἀλήθομαι, ἵνα καθαρὸς ἄρτοςεὑρεθῶ 
Rom. 4:1 I am writing to all the churches and am insisting to everyone that I die for God of my own free will—unless you hinder me. I implore you: do not be “unseasonably kind” to me. Let me be food for the wild beasts, through whom I can reach God. I am God’s wheat, and I am being ground by the teeth of the wild beasts, that I might prove to be pure bread.
Rom. 7:3 οὐχ ἥδομαι τροφῇ φθορᾶς οὐδὲ ἡδοναῖς τοῦ βίου τούτου. ἄρτον θεοῦ θέλω, ὅ ἐστιν σὰρξ τοῦ  Χριστοῦ τοῦ ἐκ σπέρματος Δαυίδ, καὶ πόμα θέλω τὸ αἷμα αὐτοῦ, ὅ ἐστιν ἀγάπη ἄφθαρτος.
Rom. 7:3 I take no pleasure in corruptible food or the pleasures of this life. I want the bread of God, which is the flesh of Christ who is of the seed of David; and for drink I want his blood, which is incorruptible love.
Apostolic Fathers: Greek Texts and English Translations
Edited and revised by Michael W. Holmes
Copyright ©1992, 1999 by Michael W. Holmes
from reading more Ignatius, its also possible he is ephasizing the word "ONE", Ignatius clearly sees to make it highly important follow the Bishops, he could be saying that Christian unity with the Bishop (thus breaking the one and the same bread) is the "medicine of immortality"."breaking one and the same bread, which is the medicine of immortality, and the antidote to prevent us from dying, but [which causes] that we should live for ever in Jesus Christ."
Interesting point. Asking what is necessary for salvation come from a very western Christian theological way of thinking (I'm speaking as an Eastern Orthodox Christian). The answer doesn't alway seem clear to some. The Scriptures point out that baptism saves. That we must forgive others to be saved. That we must believe in Jesus Christ to be saved. That we must love others to be saved. That we must feed the hungry, clothe the naked and visit the sick and imprisoned to be saved. That we must eat His flesh and drink His blood to have everlasting life. As an Orthodox Christian we say that we must do all of these - or none.The necessity for salvation would cause problems with Jesus response to the thief on the Cross.
Luke 23:43 καὶ εἶπεν αὐτῷ· ἀμήν σοι λέγω, σήμερον μετ᾿ ἐμοῦ ἔσῃ ἐν τῷ παραδείσῳ.
Thats a good point. I spent some time yesterday looking at Ignatius discussion of εὐχαριστία.from reading more Ignatius, its also possible he is ephasizing the word "ONE", Ignatius clearly sees to make it highly important follow the Bishops, he could be saying that Christian unity with the Bishop (thus breaking the one and the same bread) is the "medicine of immortality".
Phila. 4:1 Σπουδάσατε οὖν μιᾷ εὐχαριστίᾳ χρῆσθαι· μία γὰρ σὰρξ τοῦ κυρίου ἡμῶν Ἰησοῦ Χριστοῦ, καὶ ἕν ποτήριον εἰς ἕνωσιν τοῦ αἵματος αὐτοῦ· ἕν θυσιαστήριον, ὡς εἷς ἐπίσκοπος, ἅμα τῷ πρεσβυτερίῳ καὶ διακόνοις, τοῖς συνδούλοις μου· ἵνα ὃ ἐὰν πράσσητε, κατὰ θεὸν πράσσητε
Apostolic Fathers: Greek Texts and English TranslationsPhila. 4:1 Take care, therefore, to participate in one eucharist (for there is one flesh of our Lord Jesus Christ, and one cup which leads to unity through his blood; there is one altar, just as there is one bishop, together with the presbtery and the deacons, my fellow servants), in order that whatever you do, you do in accordance with God.