One of the frequent objections to taking Communion is that we are unworthy, that sin still sits in our hearts and thus we must refrain until we get rid of all our sin. John Calvin strips this objection of all its power. In fact, he argues that our sin is the exact reason we need to come to the Table.
When we feel within ourselves a strong dislike and hatred of all sin, proceeding from the fear of God, and a desire to live well in order to please our Lord, we are fit to partake of the Supper, notwithstanding of the remains of infirmity which we carry in our flesh. Nay, if we are not weak, subject to distrust and an imperfect life, the sacrament would be of no use to us, and it would have been superfluous to institute it. Seeing, then, it is a remedy which God has given us to help our weakness, to strengthen our faith, increase our charity, and advance in all holiness of life, the use becomes the more necessary the more we feel pressed by the disease; so far ought that to be from making us abstain. For if we allege as an excuse for not coming to the Supper, that we are still weak in faith or integrity of life, it is as if a man were to excuse himself from taking medicine because he was sick. See then how the weakness of faith which we feel in our heart, and the imperfections which are in our life, should admonish us to come to the Supper, as a special remedy to correct them.” (Calvin, Treatises on the Sacraments, p. 178-179)