I believe Connection between Gideon and barley bread have many spiritual significances.
1) Jesus said I am the Bread of life (John 6:35). In the bible bread speaks of the word of God which feeds believers.
2) Jesus fed the 5000 men with barely bread and had left over (John 6).
This barely bread represents message of the new covenant ,message of grace, message of good news. Jesus came to reveal the grace of God.
3) Why barely bread left over? According to Leviticus 5:16 God commands that when you offer the guilt offerings you are to add a fifth of the value in order to make restitution for the the sins you have committed. When Jesus came suffered and died he met the all the requirements of the Leviticus law. He fulfilled all the demands of the law for us. When he suffered and died he made an overpayment for our sins of the past, present, and future. No matter how many sins we commit they are covered by the blood of Jesus. More than enough to cover since he made overpayment. I believe God made this law to assure us that we shouldn't fear that our sins are too many to receive forgiveness. Message of grace reveals God's abundant love and forgiveness, always abundant left over.
4) Barley was harvested early springs (March-April) during the Passover time according to Jewish festival (Ruth 1:22) and Easter time for christian.
5) Leviticus 27:16 God commands here that barely should be measured "fifty shekels of silver to a homer of barely seed" fifty is connected year of the Jubilee and silver is related redemption. God values barley highly because it represents message of redemption and freedom. Barley bread represents the message of redemption and forgiveness.
6) connection between Gideon and barely? Old Testament characters represent Jesus and his ministries. They are illustrations and symbolic of what he does in our lives.
7) "a round loaf of barely" represents the message of grace and God's
redemption through Jesus. It is the message of grace that will strike blow on Midianite camp in our lives: "this can be nothing other than the sword of the Gideon" (Judges 7:14). Here sword speaks of the word of God: 'the sword of the Spirit which is the word of God' (Ephesians 6:17).
8) God is telling us that Midian in our lives will be destroyed and removed by the message of Grace spoken by Jesus. Message of grace, unmerited, unearned, undeserved favor of God has power to destroy sin in our lives: "for sin shall not be your master, because you are not under the law but under grace" (Romans 6:14). When we live under grace of God, the Holy Spirit empowers and enables us to overcome our sinful tendency and gives us victory over sin.
I hope this helps!
Of Barely bread--" Josephus (Jewish historian) helps us to see the significance of the symbol by adding "which men can hardly eat for its coarseness." It must be remembered that the Israelites had been reduced to such poverty by these raids that the mass of them would have nothing to subsist on but common barely bread....
Among the Greeks also "barely bread" was proverbial as a kind of food hardly fit to be eaten....."A cake of barely bread" would therefore, naturally recall the thought of the Israelites, who were no doubt taunted by their enemies with being reduced to this food...."If the Midianites were accustomed to call Gideon and his band 'eater of barely bread' often do to ridicule their enemies, the application would be the more natural" ( these are excerpts from Elliott's commentary for English readers- Bible Hub)
Dreams were recognized as Divine revelation in O.T time. I believe God used this dream to communicate His plan and will regarding the outcome of the battle to encourage Gideon and to warn Midianites. Both Gideon and the Midianites soldier understood the meaning of the dream since God chose the image that they could clearly relate. God's desire to communicate his plan to strength his people as well as warning to those who oppose his will is clearly portrayed here. I personally think that the soldier who had a dream became fearful due to divine revelation he received.
Gideon already accepted God's call to be the deliverer of Isreal and the man who had this dream knew who Gideon was since he spoke about Gideon's background information.