Where does one draw the line between spritiual attack and spiritual defense?

When truth is the matter (and it is, when we talk about God and religion), it's easy (and just) to see propagation of worldview A as an attack to worldview B. This is worsened by false images of others' beliefs, as Kurosch wrote.

Two things make difference: the way how you present the truth (your faith in the Truth, Jesus Christ) and your audience's prejudice. These are joint vessels: the more prejudice in the others, the more carefully you have to act. I would suggest you to avoid such phrases (for you, statement like "I have armor of faith" or "Jesus comes" are not meaningless phrases, but how could they understand?) and focus on "neutral" chatting and questions. When you try to understand the others beliefs, they would be more likely to listen to you, and you will more easily explain your faith in a way they can understand. To apologize your faith might be good to persuade a reasonable people (when they really calm down), but in the first time they usually even more enrage them. In face-to-face situation, I would suggest listening, staying quiet and praying for the other person and for guidance of Holy Spirit, until a) you find out what to say and b) they calm down. Then (or during their offensive) you can ask questions about their beliefs, their motivations and their assumptions about your faith. Ideally, you will help them to realize they have beaten the void, that they critised their assumptions about Christianity and not real Christianity itself. Sometimes even direct attack helps to achieve this goal, but it's risky and you must be extra sure it's from Holy Spirit, and don't try it if you don't have enough practice of peaceful discussion about religion, asking questions and listening to your opposition. In medieval disputations, the side who attacked more strongly rarely won, but the one who understood the other's position better usually was the winner.

This assumes that you are able to keep calm. If you are hurt by their verbal attacks too much (and try to protect yourself too much), how can they believe that you are not the fanatic they assumed you to be? Test your heart - if you can't bear attacking your faith, try to avoid these situations and to get stronger yourself. Pray for them, try to understand your faith deeper and deeper and try to understand their position. Few tips to consider: - What you see as attack might bee seen a a defense by the other side. Defence is not solution, understanding is the solution. - Mother Teresa (not exact citation, just as I remember it): "For a long time I thought I have to convert others. Then I realised I have to love them and it's up to God to convert them." - God is greater than anyone mocking Him. Remeber Jesus on the cross - he didn't reply and even though it must have hurted Him, he kept silent and died for them. - Do you know they won't become Christians later? And do you know what will help them to believe or what will keep them away from faith? Even the worst opponent can become a devout Christion - remember apostle Paul.

One more thing: timing matters too. There is a evangelisation technique called "traffic light" - almost everyone is open to talk about religion (and to listen to the other side), but not always. When the person is not in the mood for profound talking and thinking ("red light"), any mention of your faith only disgusts or enrages the person. Sometimes green light is on and the person is ready to discuss questions of faith. It doesn't have to be easy, still they can be critical, but it's much better. It's not easy to guess which light is on (especially for not very empathic beginers) and it's even more difficult through internet, so your poster might have just arrived to their "red mood".

I'm coming from a United Methodist tradition, if that makes a difference

The disciples asked Jesus why he spoke in parables. He replied in Matthew 13:11-13 (NRSV)

[Jesus] answered, ‘To you it has been given to know the secrets of the kingdom of heaven, but to them it has not been given. For to those who have, more will be given, and they will have an abundance; but from those who have nothing, even what they have will be taken away. The reason I speak to them in parables is that “seeing they do not perceive, and hearing they do not listen, nor do they understand.”

Jesus didn't want to take away from those who have nothing.

In other words, Jesus kept his audience in mind when he spoke about spiritual things.

Now, I'm assuming you have more than 2 Facebook friends. I would say that you could post spiritual thoughts on Facebook, and you gave the justification.

I stated that the aim of uploading this picture was to share the love of Christ, regardless of their acceptance of it, and to be fair, if they didn't want to accept it, they could have just ignored it, right?

Right, except that you also confessed this thought.

I knew before I posted it that I would likely receive spiritual attack from this...

I don't mean this as personal spiritual guidance, but the question you (all of you) have to ask yourselves is, "Am I taking away from those who have nothing?"

Edited to add TRIG's comment (which I believe goes to the "heart" of posting):

If the thought foremost in your mind as you uploaded that picture was other people's negative reactions to it, then you weren't actually doing it to "show your love of Jesus". You're just fooling yourself. On the other hand, if you uploaded it joyfully, with other people's negative reactions very much in the back of your mind, then you're probably okay.