Adam Clarke on Psalms 119:120

My flesh trembleth for fear of thee - I know thou art a just and holy God: I know thou requirest truth in the inner parts. I know that thou art a Spirit, and that they who worship thee must worship thee in spirit and in truth; and I am often alarmed lest I fall short. It is only an assurance of my interest in thy mercy that can save me from distressing fears and harassing doubts. It is our privilege to know we are in God's favor; and it is not less so to maintain a continual filial fear of offending him. A true conception of God's justice and mercy begets reverence.