Jesus, in the Sermon on the Mount, begins to introduce a new relationship for the believer—the Sonship of the believer and the Fatherhood of God. This is not the Fatherhood of God and the brotherhood of man in the liberal tone. We have lost our relationship to God as Father by sin. However, it is restored in Jesus Christ. Those who are saved restore their relationship to the Father. Jesus demonstrated this in His relationship with the Father; then, He introduced that same relationship to the believers.
Salt is necessary for life, but too much salt kills. Jesus used salt as a picture of how a small minority in the world accomplishes a great deal of good and what happens when that salt loses its saltiness.
Even in the Old Testament, much of the relationship between God and His people was based on love. God definitely loved them and they were expected to respond to Him in like kind. Yet, as today, when they began to waver from the Lord, God started getting their second-best. They gave Him the leftovers.
Christ the Firstfruits
