Whenever I read John 1:18 it seems to me like a polemic against Moses. It states:
No one has seen God at any time; the only begotten God who is in the bosom of the Father, He has explained Him.
Θεὸν οὐδεὶς ἑώρακεν πώποτε· μονογενὴς θεὸς ὁ ὢν εἰς τὸν κόλπον τοῦ πατρὸς ἐκεῖνος ἐξηγήσατο.
This text claims that (1) no one has seen God; (2) except the “only-begotten God”; and (3) this “only begotten God” is in the “bosom” of the Father and has “exegeted” or “explained” God the Father.
Exodus 33:17-23 seems to present Moses as someone who has “seen God”. It reads:
The Lord said to Moses, “I will also do this thing of which you have spoken; for you have found favor in My sight and I have known you by name.” Then Moses said, “I pray You, show me Your glory!” And He said, “I Myself will make all My goodness pass before you, and will proclaim the name of the Lord before you; and I will be gracious to whom I will be gracious, and will show compassion on whom I will show compassion.” But He said, “You cannot see My face, for no man can see Me and live!” Then the Lord said, “Behold, there is a place by Me, and you shall stand there on the rock; and it will come about, while My glory is passing by, that I will put you in the cleft of the rock and cover you with My hand until I have passed by. “Then I will take My hand away and you shall see My back, but My face shall not be seen.” 
The anthropomorphisms of this passage allow for some interesting interpretive options. What does it mean to see God’s backside, but not his face? God tells Moses that to see his face is to die.
Moses is part of the discussion in John 1. In 1:14 the Logos/Word becomes flesh (σὰρξ ἐγένετο), tabernacles among “us” (Israel? Humanity? ἐσκήνωσεν ἐν ἡμῖν), and he seen by the author(s) of the Prologue. John the Baptist is cited as a witness toward Jesus’ exalted status. The community adds their witness as having received Jesus’ “fullness” of grace. Then the author(s) says that Moses gave the Law, but Jesus the Messiah brought grace (ἡ χάρις) and truth (ἡ ἀλήθεια). Does this mean Moses did not bring grace and truth? Is the first part of that combination in need of emphasis, i.e., Moses did bring truth, but not grace?
In Exodus 34:1ff. the former tablet that contained the Law are replaced now that Moses has seen the backside of God. This leads me to think that the author had this passage in mind when he juxtaposed Jesus and Moses. What is the message of John 1:14-18 as regards Jesus, Moses, the Law, and this narrative here? Thoughts?
 New American Standard Bible: 1995 Update, Jn 1:18 (LaHabra, CA: The Lockman Foundation, 1995).
 Barbara Aland, Kurt Aland, Matthew Black et al., The Greek New Testament, 4th ed., 248 (Federal Republic of Germany: United Bible Societies, 1993).
 There are some textual differences here. Some texts read “the only begotten Son”. Some texts read “the only begotten one”. The NA27 editors felt that the evidence for “the only begotten God” was the best reading. This is maintained in the NA28.
 New American Standard Bible: 1995 Update, Ex 33:17–23 (LaHabra, CA: The Lockman Foundation, 1995).
 In addition, one may ask what it means to see the “glory” (MT: כבדך ; LXX: δόξαν) of God!