What I set out below is written as a reflection on how we can go off the rails as Christians, as well as trying to understand how religion can motivate terrible acts of violence.
"Pleasing" God can be a powerful motivator.
Once religion is embraced, and some sort of understanding of who God is, occurs, an individual may then take on all forms of devotion in a relatively short time, with relatively immature, biased and unbalanced assumptions. Assumptions that may have originated in childhood interpretations of religious stories, or childhood experiences within a religious group.
As the individual becomes caught up in the headiness of these spiritual emotions, they/we are relatively open/vulnerable to more extreme understandings of the religion.
Human pride/competitiveness leads ever so subtly into aiming "high" with our devotion, wanting to achieve a high level of "holiness" (good standing with God/pleasing God) as quickly as possible.
We easily become enchanted by those we perceive as "prophets" or "high priests".
People who seem wise, devoted and close to this God whom we have quickly become attracted to.
Those people become knowingly or unknowingly our leaders, examples, teachers and strong influencers. They stand as Gods representatives to us, and we (in this newly converted state) give them power over us. If they suggest an action or habit, we are quick to take it up, with little question, as we have put our trust in them having some belief that they are acting in God's behalf as far as our lives are concerned. We dress like them, speak like them, quote them and often think of them. We may eventually wish to replace them.
If we have a competitive nature, and there are other devotees with us in our new found faith, we will at some point, take hold of a vision or goal to do more than our devotee peers. To stand out from the crowd, to possibly become noticed/noted by our leader, to please our leader and thereby please our God whom we have become devoted to. But as God is all knowing, even if our leader does not notice, God does.
If the leader is truly wise and Godly, he or she will recognise the issue, and carefully advise the devotee that they are on the wrong track, that they themselves are not Gods personal representative to them, and that they are in fact fallible and imperfect as all of us are.
However if the leader themselves is basking in what they interpret as God given authority and influence, they may encourage the devotee to continue in ever greater degrees of self sacrifice in the pursuit of loving and pleasing God.
In some people's understanding this would mean giving up relationships with family/loved ones, giving up well payed jobs, giving up social status among "regular" peers, accepting criticism from those who are in our understanding, spiritually blind, as once we were ourselves.
Certainly a sense of converting others to our new found faith is present and compelling, but it may not stop there.
In all religions there are extreme minorities.
Amongst Christians it may involve joining a cult. Separating oneself from normal society and joining those who have a "higher" understanding and deeper devotion than we have ourselves. And thence engaging and joining in extreme expressions of that particular religion, as a way of both gaining acceptance by that group, as well as what we perceive as pleasing God.
I suspect this is the road to extremism and potentially serious acts of violence towards "unbelievers".