So what does it mean to be salty? It means that Christ's disciples engage with society to work toward flourishing of people, communities and the environment. Most current studies demonstrate that economic well-being is achieved when communities are "healthy." That is they evidence a high degree of trust amongst its members, they work toward the common good, and there are strong informal networks of association. Good works are those which help achieve human, community, environmental, and economic thriving. When communities thrive we could say "the kingdom of heaven is being realized here on earth." The truth of God infuses these good works, so the Father in Heaven is glorified.
Christ calls us to be transformed by His light to orient rightly to be salt. We can test correct orientation by asking four questions outlined by Oliver O'Donovan in his book Resurrection and Moral Order: 1) does our ethical engagement respect God's created order; 2) does our ethical engagement respect the law as fulfilled in Jesus Christ; 3) is our ethical engagement light for the world; 4) does our ethical engagement glorify God. When our saltiness is formed from God's truth, God is glorified and our ethical engagement honors His created order. God created all things and His created agency of love is infused into the created order. Our saltiness is not salty when we oppose His created agency which flows from His love.
So how can we be sure our saltiness is filled with light? First pray for issues which confront us every day. There are a multitude of issues in the news every day. Which ones resonate in your heart? Bring those issues to God in prayer. Prayer shapes our will by His will. Secondly, study. Study Scripture for His revelation and understanding concerning His creation and our relationship to Him, to each other, and to the world around us. Read other sources and not just those authors which agree with voices in your own head. Third, listen. Listen to the voice of the oppressed and those who speak for them when their voices are silenced by oppression. Fourth, get the facts. Be sure the information you are receiving is accurate. Check reputable and multiple sources. Fifth, engage. Find out how God wants you to engage with the issues He has placed on your heart. Lastly, come back to prayer. Pray for how you responded and future directions to take. Mobilize others to pray with you and to participate in engagement.
Jesus challenges His disciples that we don't live in a vacuum. Be salt infused with light so that your good works so shine before others that the Father in Heaven is glorified.