Everyone is in different places of spiritual growth & trials for one thing. I can very easily remember being pretty "guarded".. it's a defense. We aren't made with a default setting to automatically trust anyone... even God. I used to always expect the worst, and hope for the best - then no matter what, I wouldn't be disappointed. It's flawed thinking... but we're flawed humans

We have to
learn.... what to think, what to do, how to act & react, etc. We have to learn that our emotions & feelings are very easy targets for satan. Anything that causes an emotional reaction or strong feeling makes us vulnerable to temptation/attack. For me, it's like an alarm system that goes off... if I find I'm having some sort of emotional reaction, I try to just stop. Be still. Pray. And then re-focus. If I don't, then I might say or do something that isn't quite wise, loving, or right in God's eyes.
One of the hardest things to overcome for me, was/is thoughts. There are quite a few verses of scripture on thinking... and for me, it basically came down to survival. I
had to be able to control thoughts/emotions and not allow them to be used against me!
And just because someone is saved, doesn't mean there isn't a battle. That enemy will try all kind of tricks and traps to get at us. We have to be prepared. Scripture tells us this.
-Sorry for rambling around... that probably didn't even come close to answering your question..