In sensus plenior:
Bread represents the body of Christ and the cross, and "every word which proceeds from the mouth of God" is represented by fish.
Bread as the cross
Bread represents the cross, because Jesus said it represented his body after having broken it , and Paul interprets it by saying "broken for you" though Jesus's body was not broken on the cross. The riddle (apparent contradiction) is solved this way:
All of the things which were parted, broken and torn are symbols of the cross where the Father is separated from the son. 
Three testimonies of the Word on earth
1Jo 5:8 And there are three that bear witness in earth, the Spirit,
and the water, and the blood: and these three agree in one.
Three testimonies are related to the methods by which we respond to God, or don't.
The Spirit testifies to us by way of general revelation and by the still small voice that draws us to God. Like the sheep who hear the shepherds voice and recognize it, though they don't understand the words, we hear God, or we are deaf.
The water, as the propositional word of God containing expressions of Holiness and Grace, we see the works of God in a manner which may be understood intellectually. Or we are blind.
Since the "life is in the blood", the testimony of the blood is the very life of Christ as the incarnate Word, revealing to us those things which are beyond hearing and seeing. We can walk with Christ, meaning to live in him, or we are lame.
Fish as the Word
Christ is the ante-type of the clean fish
- He wears the full armor of God, (the word for scales means armor)
- He lives (swims) in the Word (water)
- He is devoured by the lobster which is an abomination. (The lobster lives in the earthly bottom and snatches fish to devour them.) Men, working in the flesh, put Christ to death.
Jesus fed bread and fish together
Jesus said that man does not live by bread alone, but by every word which proceeds from the mouth of God.
In other words, man does not live by the cross alone, but by the word revealed By the Spirit, the water and the blood... the whole word of God.
Joh 3:3 Jesus answered and said unto him, Verily, verily, I say unto
thee, Except a man be born again, he cannot see the kingdom of God.
One cannot see (understand) the Kingdom of God until the second birth which comes through the cross (bread). But we cannot live by bread alone.
Keep my commandments
Jesus says that if we love him, we are to keep his commandments 
In saying this, he is simply teaching what was taught in the scriptures: that we should love God and keep His commandments. 
The connection between manna and the word
Manna is the bread which gave Israel life and which gives sinners life, representing the cross. Symbolically, Israel was called out of Egypt/the world and spent 40 years in a desolate place (like Christ in the tomb) and did not see the promised land (the kingdom of God) until they were "born again" by crossing the Jordan as a type of Christ's resurrection.
The manna is what sustained them keeping them from 'tasting death', and the Word of God is what keeps us living in the Kingdom of Heaven. The manna makes us born-again, while we "walk in the word". 
The bread gives life, the fish sustain it.
See how the metaphoric meanings are reusable:
The stone is the Word of God expressing the Law and the serpent the original liar.
Lu 11:11 If a son shall ask bread of any of you that is a father, will
he give him a stone? or if [he ask] a fish, will he for a fish give
him a serpent?
Paraphrase: If your son asks for mercy (the cross) will you give him the law?
If he asks for "every word which proceeds from the mouth of God" will you give him a lie?
They are reusable because they must mean the same thing everywhere they occur, since they are written by the same author (God). This cross-linking and locking is what makes the meaning of a sensus plenior interpretation sure.
Mt 26:26 And as they were eating, Jesus took bread, and blessed it,
and brake it, and gave it to the disciples, and said, Take, eat; this
is my body.
Mr 14:22 And as they did eat, Jesus took bread, and
blessed, and brake it, and gave to them, and said, Take, eat: this is
Lu 22:19 And he took bread, and gave thanks, and brake it,
and gave unto them, saying, This is my body which is given for you:
this do in remembrance of me.
1Co 11:24 And when he had given thanks, he brake [it], and said, Take,
eat: this is my body, which is broken for you: this do in
remembrance of me.
Mt 27:46 And about the ninth hour Jesus cried with a loud voice,
saying, Eli, Eli, lama sabachthani? that is to say, My God, my God,
why hast thou forsaken me?
Mr 15:34 And at the ninth hour Jesus cried
with a loud voice, saying, Eloi, Eloi, lama sabachthani? which is,
being interpreted, My God, my God, why hast thou forsaken me?
Joh 14:15 If ye love me, keep my commandments.
Joh 14:21 He that hath my commandments, and keepeth them, he it is
that loveth me: and he that loveth me shall be loved of my Father, and
I will love him, and will manifest myself to him.
Joh 15:10 If ye keep my commandments, ye shall abide in my love; even
as I have kept my Father’s commandments, and abide in his love.
1Jo 5:2 By this we know that we love the children of God, when we
love God, and keep his commandments.
1Jo 5:3 For this is the love of God, that we keep his commandments:
and his commandments are not grievous.
2Jo 1:6 And this is love, that we walk after his commandments. This
is the commandment, That, as ye have heard from the beginning, ye
should walk in it.
Ex 20:6 And shewing mercy unto thousands of them that love me, and
keep my commandments.
De 5:10 And shewing mercy unto thousands of
them that love me and keep my commandments.
De 7:9 Know therefore
that the LORD thy God, he is God, the faithful God, which keepeth
covenant and mercy with them that love him and keep his commandments
to a thousand generations;
De 11:1 Therefore thou shalt love the LORD
thy God, and keep his charge, and his statutes, and his judgments, and
his commandments, alway.
1Ki 2:4 That the LORD may continue his word which he spake concerning
me, saying, If thy children take heed to their way, to walk before me
in truth with all their heart and with all their soul, there shall not
fail thee (said he) a man on the throne of Israel.
1Ki 6:12 Concerning this house which thou art in building, if thou
wilt walk in my statutes, and execute my judgments, and keep all my
commandments to walk in them; then will I perform my word with thee,
which I spake unto David thy father:
Isa 2:3 And many people shall go and say, Come ye, and let us go up
to the mountain of the LORD, to the house of the God of Jacob; and he
will teach us of his ways, and we will walk in his paths: for out of
Zion shall go forth the law, and the word of the LORD from Jerusalem.
Isa 30:21 And thine ears shall hear a word behind thee, saying, This
is the way, walk ye in it, when ye turn to the right hand, and when ye
turn to the left.
Mic 4:2 And many nations shall come, and say, Come, and let us go up
to the mountain of the LORD, and to the house of the God of Jacob; and
he will teach us of his ways, and we will walk in his paths: for the
law shall go forth of Zion, and the word of the LORD from Jerusalem.