Isa 32:17 The work of righteousness will be peace, And the effect of righteousness, quietness and assurance forever.
A lot of people are troubled, distressed and worried sick about their condition before God. They don't have peace, they don't have quietness and they are uncertain.
Their consciences, like a sore tooth, nag them to no end on and on. They want peace, quietness and certainty, but they can only have it if they are right with God. They are wrong and so they must be right with God.
Peace, tranquility and certainty are the products and effects of having a right standing with God.
And they can only have this right standing with God through faith in Christ Jesus.
Ro 5:1 Therefore, having been justified by faith (in the Savior), we have peace with God through our Lord Jesus Christ