This proposition also is in a manner self-evident.
For 1st, That the practice of virtue or vice must be attended with rewards and punishments, proved from the attributes of God. If God is himself necessarily a being (as has been before shown) of infinite goodness, justice, and holiness; and if the same reasons which prove the necessity of these attributes in God himself, prove moreover (as has likewise been shown already,) that the same moral obligations must needs be his positive will, law, and command, to all rational creatures; it follows also necessarily, by the very same argument, that he cannot but be pleased with and approve such creatures as imitate and obey him by observing those rules, and be displeased with such as act contrary thereto. And if so; then in the nature of the thing itself it is evident, that having absolute power and uncontrollable authority, as being supreme governor and disposer of all things, he cannot but signify, by some means or other, his approbation of the one, and his displeasure against the other. And this can no way be done to any effectual purpose but by the annexing of respective rewards and punishments. Wherefore, if virtue goes finally unrewarded, and wickedness unpunished, then God never signifies his approbation of the one, nor his displeasure against the other; and if so, then there remains no sufficient proof that he is really at all pleased or displeased with either, and the consequence of that will be, that there is no reason to think the one to be his will and command, or that the other is forbidden by him; which being once supposed, there will no longer remain any certain evidence of his own moral attributes contrary to what has been already demonstrated.
2. And from the necessity there is, that there should be some vindication of the honour of God's laws and government. The certainty of rewards and punishments in general may also somewhat otherwise be deduced from their being necessary to support the honour of God and of his laws and government, in the following manner. It is evident we are obliged, in the highest ties of duty and gratitude, to pay all possible honour to God, from whom we receive our being, and all our powers and faculties, and whatever else we enjoy. Now it is plain likewise, that we have no other way to honour God, (whose happiness is capable of no addition from any thing that any of his creatures are capable of doing,) than by honouring, that is, by obeying, his laws. The honour therefore that is thus done to his laws, God is pleased to accept as done immediately to himself. And though we were indeed absolutely obliged, in duty, to honour him in this manner, notwithstanding that there had been no reward to be expected thereupon, yet it is necessary, in the government of the world, and well-becoming an infinitely wise and good governor, that those who honour him he should honour; 1 Sam. ii.30. that is, should distinguish them with suitable marks of his favour. On the contrary; though nothing that weak and finite creatures are able to do, can in the least diminish from the absolute glory and happiness of God, yet, as to us, the dishonouring, that is, the disobeying his laws, is a dishonouring of himself: that is, it is, as much as in us lies, a despising his supreme authority, and bringing his government into contempt: -- Now the same reason that there is, why honour should be paid to the laws of God at all; the same reason there is, that that honour should be vindicated, after it has been diminished and infringed by sin: For no lawgiver who has authority to require obedience to his laws, can or ought to see his laws despised and dishonoured, without taking some measures to vindicate the honour of them, for the support and dignity of his own authority and government. And the only way, by which the honour of a law, or of its author, can be vindicated after it has been infringed by wilful sin, is either by the repentance and reformation of the transgressor, or by his punishment and destruction. So that God is necessarily obliged, in vindication of the honour of his laws and government, to punish those who presumptuously and impenitently disobey his commandments. Wherefore if there be no distinction made by suitable rewards and punishments, between those who obey the laws of God and those who obey them not, then God suffers the authority of his laws to be finally trampled upon and despised, without ever making any vindication of it: Which being impossible, it will follow that these things are not really the laws of God, and that he has no such regard to them as we imagine. And the consequence of this must needs be the denial of his moral attributes, contrary, as before, to what has been already proved: And consequently the certainty of rewards and punishments, in general, is necessarily established.