My main function as a Christian is to be the biggest possible jerk as a demonstration of the awe found in God's Grace and Forgiveness. (That love part comes in to play at some point)
It will be interesting to see what the motive was. It is doubtful the shooter(s) were just driving down the street bored and suddenly decided to stop in at the Sikh temple and shoot a bunch of people. It is certainly possible that the shooter lived nearby and was angry because the Sikh's caused extra traffic on Sunday or maybe there was a boundary dispute over adjoining property. If there was security in place it doesn't seem at this point that they recognized the shooter(s).
Knowing that Sikhs - who have nothing to do with terrorism, and had nothing to do with 9/11 - have experienced a noticeable increase in hatred and personal attacks from white people here in the US, you'd think they would have increased security. While I have been to Hindu temples, I have not been to a Sikh temple, though I have a standing invitation. From what I understand Sikhs welcome all people as they view all people, men and women, all religions as equal. That openness and respect for all people isn't such a good thing when you are trying to secure a place of worship.
But the reality is that these things happen in every society.
Japan has many mass stabbings.
Crazy, alienated people with extreme levels of anger directed at the outside world will find a way to put their hate into action. It doesn't have to be a gun. Oklahoma City, for example? No one shot there. 168 people still died.