Paul writes in Ephesians 5:20 that "We are therefore Christ's ambassadors". An ambassador is someone who no longer speaks only for themselves, but speaks on behalf of the government, the king or queen, the people and the country they represent. They have to think of everything they say and do in terms of how it reflects not only on them, but on everyone they represent, as an authorised messenger for those people.
Being an ambassador for a country is a huge honour, and carries with it great responsibility. But as ambassadors for Jesus Christ we have an even greater responsibility and honour, representing and being messengers for Him in all we say and do. We need to be aware of this in all of our lives, but I believe in particular with what we do online, as the things we choose to blog, tweet and put on Facebook are available for anyone to see, and once written are almost impossible to remove. That means they can leave an even more indelible mark than the things we say verbally.
So what does that mean for us practically?
First we need to make sure that everything we say online reflects well on God and honours Him, That doesn't mean that everything that we post online has to be bland, unquestioning, sugary or just plain "nice". It's possible to write about our doubts, worries, questions and fears in a way which is authentic but which still honours God - if you don't believe me just spend some time reading the Psalms! They manage to express some of the darkest human emotions, and biggest questions of life, in a way which still rightly recognises who God is. But let's focus on the incredible blessings of our relationship with God, answers to prayer, encouragements and verses which inspire us.
Secondly we need to represent our church, and other churches, well. If we have disagreements or questions about what is going on in church, let's not play out our disagreements in a public forum. And let's make sure we honour leaders in our community in what we say online (see 1 Timothy 5:17). There is so much positive going on for us to talk about, and so much to celebrate, so let's talk about those things, as people will be reading what we write online when making deciding what they think about the church. That's not to say we can't challenge other people online, especially if what they've made their comments publicly. For an example of how to do this well see how Dave Gilpin reviewed Rob Bell's controversial book "Love Wins", or take a look at what Vicky Beeching had to say about discussing theology on social media.
Thirdly let's represent one another well, always thinking the best of, and wanting the best for one another. Let's not pull one another down or criticise one another online, but choose to build one another up and encourage one another. And let's be aware of our audience when we write - there may be some things you'd be happy to say to an adult audience, but not to all the teenagers who may be your friends on Facebook.
The bottom line. As a Christ follower, when you speak you no longer just speak for yourself but you speak as a representative of God and His kingdom. That's an awesome privilege, but also an incredible responsibility.