The measure of our love to God, seems in justice to be the measure of our love of every virtue. We are to love and practise it with all our heart, with all our soul, with all our mind, and with all our strength. And when we cease to live with this regard to virtue, we live below our nature, and, instead of being able to plead our infirmities, we stand chargeable with negligence.
It is for this reason that we are exhorted to work out our salvation with fear and trembling; because unless our heart and passions are eagerly bent upon the work of our salvation; unless holy fears animate our endeavours, and keep our consciences strict and tender about every part of our duty, constantly examining how we live, and how fit we are to die; we shall in all probability fall into a state of negligence, and sit down in such a course of life, as will never carry us to the rewards of Heaven.
And he that considers, that a just God can only make such allowances as are suitable to His justice, that our works are all to be examined by fire, will find that fear and trembling are proper tempers for those that are drawing near so great a trial. And indeed there is no probability, that any one should do all the duty that is expected from him, or make that progress in piety, which the holiness and justice of God requires of him, but he that is constantly afraid of falling short of it.
Now this is not intended to possess people’s minds with a scrupulous anxiety, and discontent in the service of God, but to fill them with a just fear of living in sloth and idleness, and in the neglect of such virtues as they will want at the day of Judgment. It is to excite them to an earnest examination of their lives, to such zeal, and care, and concern after Christian perfection, as they use in any matter that has gained their heart and affections.
William Law, A Serious Call to a Devout and Holy Life (pgs. 13-14).