Passion for Christ

I always feel guilty that I have this question in my mind and heart.
As I grow in Christ, I begin to question myself and those I see around me, whether when we worship, are we lip-singing or singing with a distracted mind or singing with no one in mind? 
I tend to question the sincerity of our heart. 
Is it a show? 
Is it a duty or is it a passionate cry for God?
Perhaps God put all these questions in my mind cos I'm easily distracted when I worship. 
I need to pray really hard to focus on Him. 
And it's only after I set my mind and heart on Him that I sense that cry in me for Him. 
Then I realise that it's not my job to speculate if any particular person worships from the heart or not.
God is asking me, "What about you? Do I not see? Do I not hear?"
It starts from me.
It is too easy to doubt a person's sincerity but we always don't doubt our own.
Even when I'm very sure of my own heart, let me not forget that our heart is easily deceived.
This does not mean we cease to be discerning of what's happening around us.
It reminds me to always give the benefit of doubt unless proven against His word.
In the end, each of us has to account to God of whom we cannot hide anything from.