One might pray and not be a Christian, but one cannot be a Christian and not pray.
It is by virtue of the atonement that God can maintain His justice and yet demonstrate His mercy.
If it were left to us, we would all fall away from the faith and perish.
No sinner has the right to say with impunity, 'God you owe me grace.' If grace is owed, it is not grace. The very essence of grace is its voluntary character. God reserves to himself the sovereign, absolute right to give grace to some and withhold that grace from others.
Doctrine does matter.
Humanism was not invented by man, but by a snake who suggested that the quest for autonomy might be a good idea.