In this Psalm, we continue to work our way from the really big scale down to a finer scale. We started with considering the size of the universe. Then the Psalm focused on God's blessings on our own planet. In the last few verses, the Psalm focused on the true source of power. The true power is God, as opposed to our own strength or that of strong animals.
Now we get back to Jerusalem. One has to remember that for a Jewish believer, the city of Jerusalem represents the specific location where those Israelites gathered to worship God. The Israelites were dependent upon Him to give peace to that city and provide for the people who gather there. Jerusalem is a city with no natural resources. In effect, it depends upon tourism (people visiting the city to worship) in order for that city to survive. The idea is that as Jewish people gathered there in order to worship God, He provides for the resident's needs and protection.
 He maketh peace in thy borders, and filleth thee with the finest of the wheat.
God even controls the productivity of the land. His blessing is described in terms of the abundance that Israel will enjoy. In fact, the phrase, "finest of the wheat" in the later part of verse 14 means that if we trust Him, He will provide through our effort for our own physical as well as our emotional needs.