The simple, standard definition of belief is simply, 'a state of mind, which one holds, in which the individual believes something to be the case without any empirical evidence'.
Belief is easy. Mustering the conviction to act according to principle is difficult.
See, we can believe all kinds of things to be true, and belief (of holding to the above definition) can facilitate this process, because it is fluid.
But to actually hold a belief, this, my friends, is when simple faith becomes conviction. This is what our society lacks. Conviction to act.
This is why I cannot take people seriously when they claim Christianity. Hell, I don't even think I can take myself seriously when it comes to that anymore.
True belief is supplemented by action. This conviction to act according to principles allows for consistency, this belief is not simply a novelty when things are going smoothly, but remains still when all is looking hopelessly bleak.
You see, when it comes to something like religion, discussing the eternal things, claiming faith and allegiance to a deity, without any sort of need to demonstrate this conviction, belief is simply an empty statement. If you aren't willing to bet the whole farm on something, you probably don't believe in it that strongly.
Instead, Christians have this nice sounding "Jesus is my personal savior and lives in my heart", "It's ok, God is just love and loves everybody" doctrine, which is accompanied by "I'm a sinner, you're a sinner, so I have no right to judge anyone or say anything that might offend" mentality. By doing this, this religion becomes completely subjective to the individual, thus negating its central tenant. Self-sacrifice. We don't make "the rules" this belief is simply predicated on whether or not one will submit...
Furthermore, if Christians in our day and age truly, I mean truly believed they carried the words of God wherever they went, then they certainly would actually know what is in between the leatherbound covers. Alas, there is no such sense of urgency.
All this to say, it is one thing to claim you believe in something or someone, it is another thing to live and act as if you do.