In opposition to (the Roman Catholic view), our forefathers not only maintained that a man is justified by faith, but that he ought to know that he is justified, and that such knowledge is the great root of a holy life. It started a man upon a happy life, because it relieved him from the burden of doubt and the gloom of uncertainty. It made his religion bright and tranquil, because it sprang so sweetly from the certainty of his reconciliation to God. It delivered him from the cruel suspense and undefined fears which the lack of assurance always carries with it.

Moreover, it rescued him from every temptation to pride, presumption, and self-righteousness, because it did not arise from any good thing in himself, but drew him away from himself to Christ–from what he was doing, to what Christ had done. Thus did it make Christ, not self, the basis and center of his new being. It made him more and more dissatisfied with self and all that self contained, but more and more satisfied with Jesus and his fullness. It taught him to rest his confidence toward God, not on his satisfaction with self, or on the development of his own holiness, or on the amount of his graces and prayers and doings, but simply on the completed work of Him with whom God is well pleased. – Horatius Bonar

Note: To read the article from which this excellent quote is taken, click here.