"'Then lie on your left side and put the sin of the house of Israel upon yourself. You are to bear their sin for the number of days you lie on your side. I have assigned you the same number of days as the years of their sin. So for 390 days you will bear the sin of the house of Israel.'" NIV translation
Imagine a man going out and laying in the street for over a year. That is what God had Ezekiel do as a symbol to the people of the northern kingdom (Israel). This was a witness to Israel of the patience of God and even though judgment was coming He had been patient as He allowed them 390 years of rebellion.
"'After you have finished this, lie down again, this time on your right side, and bear the sin of the house of Judah. I have assigned you 40 days, a day for each year.'" NIV translation
The right side is the position of inheritance and honor. God told Ezekiel to lay in the street on his right side a day for each year that Judah has rebelled (sinned against God). Judah refers to the southern kingdom where Jerusalem (the city of God) was located. Israel had rebelled for 390 years and Judah had been influenced by them and gone astray as well.
This lasted for forty years before God decreed judgment on them for their rebellion. From this, we can learn that it matters who you choose to associate with as they can influence you and your walk with the Lord.
"'Turn your face toward the siege of Jerusalem and with bared arm prophesy against her. I will tie you up with ropes so that you cannot turn from one side to the other until you have finished the days of your siege.'" NIV translation
God bound Ezekiel with ropes to demonstrate the fact that He would not change His mind about the coming destruction of Jerusalem. We have all heard about God's love and are grateful for it but we also must remember that God is just and will deliver judgment at the appointed time. This is like what Peter was talking about in his second letter to believers. (see 2 Peter 3)
"'Take wheat and barley, beans and lentils, millet and spelt; put them in a storage jar and use them to make bread for yourself. You are to eat it during the 390 days you lie on your side. Weigh out twenty shekels of food to eat each day and eat it at set times. Also measure out a sixth of a hin of water and drink it at set times.'" NIV translation
God even gave Ezekiel instructions on how he was to eat and drink during his prophecy. He lists the food and it is interesting to note that it is three groups of two things each. We remember from our studies that the number three is associated with the earthly display of God's will while the number two is the number of witnessing. With this in mind, we can see that God is going to use this diet to testify against the people.