How is the kingdom of heaven opened and shut by the preaching of the holy gospel?

By proclaiming and openly witnessing, according to the command of Christ, to believers, one and all, that, whenever they receive the promise of the gospel by a true faith, all their sins are really forgiven them of God for the sake of Christ’s merits; and on the contrary, by proclaiming and witnessing to all unbelievers and such as do not sincerely repent that the wrath of God and eternal condemnation abide on them so long as they are not converted. According to this witness of the gospel God will judge, both in this life and in that which is to come.

Article 12: This certainty of perseverance, however, is so far from exciting in believers a spirit of pride, or of rendering them carnally secure, that on the contrary, it is the real source of humility, filial reverence, true piety, patience in every tribulation, fervent prayers, constancy in suffering, and in confessing the truth, and of solid rejoicing in God: so that the consideration of this benefit should serve as an incentive to the serious and constant practice of gratitude and good works, as appears from the testimonies of Scripture, and the examples of the saints.

Article 11: But when God accomplishes his good pleasure in the elect, or works in them true conversion, he not only causes the gospel to be externally preached to them, and powerfully illumines their minds by his Holy Spirit, that they may rightly understand and discern the things of the Spirit of God; but by the efficacy of the same regenerating Spirit, pervades the inmost recesses of the man; he opens the closed, and softens the hardened heart, and circumcises that which was uncircumcised, infuses new qualities into the will, which though heretofore dead, he quickens; from being evil, disobedient and refractory, he renders it good, obedient, and pliable; actuates and strengthens it, that like a good tree, it may bring forth the fruits of good actions.

Article 12: And this is the regeneration so highly celebrated in Scripture, and denominated a new creation: a resurrection from the dead, a making alive, which God works in us without our aid. But this is in no wise effected merely by the external preaching of the gospel, by moral suasion, or such a mode of operation, that after God has performed his part, it still remains in the power of man to be regenerated or not, to be converted, or to continue unconverted; but it is evidently a supernatural work, most powerful, and at the same time most delightful, astonishing, mysterious, and ineffable; not inferior in efficacy to creation, or the resurrection from the dead, as the Scripture inspired by the author of this work declares; so that all in whose heart God works in this marvelous manner, are certainly, infallibly, and effectually regenerated, and do actually believe. – Whereupon the will thus renewed, is not only actuated and influenced by God, but in consequence of this influence, becomes itself active. Wherefore also, man is himself rightly said to believe and repent, by virtue of that grace received.