One example is when He said, "You are the salt of the earth." Traditionally, many Christians have identified themselves as the salt of the earth, but this was a covenant conversation Jesus was having with His Jewish disciples who were still under the law. A covenant of salt between men was not an uncommon idea in those times. The problem is that Israel failed the covenant God made with them, the salt lost its flavor—and needed to be thrown out (Gulp!). Nobody could attain righteousness through that covenant containing the law. The good news is that by God's grace and mercy, it would not be the people being thrown out, but the covenant would need to be tossed aside and replaced with something better.
The house of Israel was also considered the light of the world as Jesus spoke to them, but it was a light growing dim through an inconsistent effort of works of the law. Jesus later stated He was the light of the world ... and new covenant writings describe us as children of the light ... but it's His light that we reflect, which is a different position than His reference to Israel in Matthew 5.
When it comes to the teachings of Jesus, developing an understanding of the Old and New Covenants and their timeline will help avoid a lot of inconsistencies in what we say and what we think we believe.
