When Jesus Christ made miracles, he used the material that is available. He used the water in jars to make wine in the wedding of Cana and even mud to heal a deaf man.
In today's Gospel, when the people were hungry, Jesus told his disciples, "Give them some food yourselves." The people gave food in the form of fish and bread. Jesus blessed the food, and the food became many and satisfied the hungry people.
In the mass whenever the priest blesses or consecrates the host and wine, Jesus becomes part of the host and wine. This is called transubstation. We believe that Jesus is part of us so we live in accord with God's will.