If my heart is established, I am at peace with God, firmly convinced that God is satisfied with me and that He is pleased with men. If my heart is established, then I am convinced that the guilt and defilement of sin is removed and that I am certain for heaven as if I were already there. The question then is this – What is it that establishes my heart and gives me peace, assurance, confidence of salvation? The apostle states emphatically that "it is a GOOD thing that the heart be established with GRACE."
First of all, this is not a mystical, religious experience that takes place in ecstatic ignorance. To have our hearts established with grace is to be convinced in our minds of God's testimony of grace so much that it affects our whole lives, our wills, our affections. God's testimony of grace is that He will surely save sinners based on the imputed righteousness of Christ and nothing else. If my heart is established upon any other ground, such as meats (this refers to any deeds of the law that sinners might think recommend them unto God), it is not a good thing but an evil thing. If my heart is established by my faith, my repentance, my obedience, my reformations, my religious experiences, anything but the imputed righteousness of Christ alone, then it is an evil thing because it is opposed to God's glory and to salvation conditioned on Christ.