Salt and Light 
Dear brother and sister, the following teaching is based on one given by another1 and the blessing was revealed by our Living God. 
Ye are the salt of the earth: but if the salt have lost his savour, wherewith shall it be salted? it is thenceforth good for nothing, but to be cast out, and to be trodden under foot of men. Ye are the light of the world. A city that is set on an hill cannot be hid. Neither do men light a candle, and put it under a bushel, but on a candlestick; and it giveth light unto all that are in the house. Let your light so shine before men, that they may see your good works, and glorify your Father which is in heaven
(Matthew 5:13-16)
Jesus, our Teacher, used the metaphors of salt and light because their qualities were known by the people of the time then, just as they are understood today, and He compared their physical properties with the spiritual ones that we are expected to fulfil as members of the Kingdom 
The order that Jesus used in the teaching was the salt first and then the light. There was a purpose behind this as we shall shortly see. 
There is a difference in the outcome of salt and light, but at the same time the purpose of salt-shakers and light bearers is the same and this is promoting the Kingdom of which we are citizens. It is something that we each must choose to do, in response to the loving Commandment of our King. 
Just as in His other teachings, the ministry of Jesus of Nazareth was to show us believers - who study His word - what is expected of us; we who are potential life changers, having the Living God residing in our bodies. 
Salt. The properties of salt as a product is firstly that it has an unpleasant taste and is only used in small amounts to add flavour to food. Secondly it is added to food on a regular basis, and thirdly is used as a preservative, especially of meat or fish such as in the making of biltong or bokkems. 
So, we Christians should be salty, sharing with others, in season and out of season, the necessity of obeying God's Commandments as we do the same, even though we are under the blessing and conditions of the New Covenant, that Jesus made with the Father on our behalf. 
For verily I say unto you, Till heaven and earth pass, one jot or one tittle shall in no wise pass from the law, till all be fulfilled. 
(Matthew 5:18)
But after thy hardness and impenitent heart treasurest up unto thyself wrath against the day of wrath and revelation of the righteous judgment of God; Who will render to every man according to his deeds: To them who by patient continuance in well doing seek for glory and honour and immortality, eternal life: But unto them that are contentious, and do not obey the truth, but obey unrighteousness, indignation and wrath, Tribulation and anguish, upon every soul of man that doeth evil, of the Jew first, and also of the Gentile; But glory, honour, and peace, to every man that worketh good, to the Jew first, and also to the Gentile: For there is no respect of persons with God. For as many as have sinned without law shall also perish without law: and as many as have sinned in the law shall be judged by the law; (For not the hearers of the law are just before God, but the doers of the law shall be justified. For when the Gentiles, which have not the law, do by nature the things contained in the law, these, having not the law, are a law unto themselves: Which shew the work of the law written in their hearts, their conscience also bearing witness, and their thoughts the mean while accusing or else excusing one another;) In the day when God shall judge the secrets of men by Jesus Christ according to my gospel. 
(Romans 2:5-16)
Light. Which property is to chase the darkness of Satan's kingdom away by our example as Christians in this present world. In other words, practising what we preach. 
1 So Jesus calls His disciples to exert a double influence on the secular community, a negative influence by arresting its decay and a positive influence by bringing light into its darkness. For it is one thing to stop the spread of evil; it is another to promote the spread of truth, beauty and goodness. 
Putting the two metaphors together it seems legitimate to discern in them the proper relationship between evangelism and social action in the total mission of Christ in the world - a relationship which perplexes many believers today. We are called to be both salt and light to the secular community. 
Please remember dear Christian, that as you give, so shall you receive, now and in the world to come. 
1 John R.W.Stott: The Messages of the Sermon on the Mount.