Jesus said to his disciples that they were the "salt of the earth" and the "light of the world" (Matthew 5:13-14). They're sayings we know so well we probably feel we don't really need to think very much about them any more.

But the Bible keeps giving more the more we read it. And one of the interesting things about these sayings is why Jesus, or why Matthew, puts them exactly here. They come immediately after the Beatitudes, the 'blessed ares' – 'Blessed are the poor in spirit", the mourners, the merciful, the pure in heart, the persecuted.

So what this seems to mean is that it's the people described in these Beatitudes that are going to be the salt of the earth and the light of the world. It isn't so much what people do, as who they are, that matters.

This is important in our own context today, when Christianity is on the defensive in many areas. Many Christians feel threatened or distressed by legislation that seems to them to be anti-Christian. Their reaction is to fight against it and seek to preserve what they believe are good laws. Being salt and light means influencing the culture and making it more like the Kingdom of God.

Others are deeply aware of the failure of the Church to connect with the next generation. They look at churches that aren't as full as they once were and feel the urgency of the need for evangelism. Being salt and light is about witnessing to Christ and persuading people to take his claims seriously.

There are dangers with both these approaches. If we get into culture wars and equate faithful discipleship with championing unpopular causes, raising petitions and influencing lawmakers, we might find ourselves become effective at politics but ineffective at being spiritual. We might win battles, but we'll lose the war for hearts and minds.

If we do evangelism because we're scared of churches emptying or we feel we need to keep our numbers up, we'll be doing it for the wrong reasons. We evangelise because we want to share the love we've been shown, not because we need to recruit replacement soldiers in God's army.

Being salt and light means being the kind of people Jesus talks about in the Beatitudes: thirsting for righteousness, merciful, peacemakers, persecuted but strong.

People like that are attractive. That's not always the image people have of Christians – in fact it's often the reverse. Christians can come across as harsh and unloving, or just not very interesting. We give the impression of people who've renounced the good things in life rather than luxuriating in them. The American judge and author Oliver Wendell Holmes once wrote: "I might have entered the ministry if certain clergymen I knew had not looked and acted so much like undertakers." The poet Algernon Swinburne, reflecting on the victory of Christianity over paganism, wrote: "Thou hast conquered, O pale Galilean/ The world has grown grey from thy breath."

But Christians who are salt and light aren't gloomy and grey. They are the most alive people of all, giving the world savour and enlightment. And it comes not from winning battles but from being a particular kind of person – the kind with the 'beautiful attitudes' Jesus has just described.

Follow Mark Woods on Twitter: @RevMarkWoods