Here we have two distinct things put together, namely, To Glorify God and Enjoy Him Forever. But we must warily consider them, else we may be greatly mistaken about them.
It is to be observed, that in strict speaking, that which is chief can be but one is a contradiction to say, there are two last ends; if both are equal, neither of them can be chief or last. Among intermediate ends some may be subordinate, others may be coordinate, but the last will admit of no compeer: and as the chief and is but one, so it is not a thing compounded, but single. It cannot be made of the meeting of divers in one; for that which is compounded is indeed manifold; and except there were an equality between those things so concurring, they cannot be of a like weight and therefore the one must needs stand in subordination to the other. So, that if we would speak exactly there is but one of these, namely, To Glorify God, which is man’s chief end; the other is immediately subordinated, or it is next to the last. It is man’s duty to seek his own best good, which consists in his enjoying of God; but he is to do it in and for the glory of God; and so from thence all his seeking of it is to take its measures.
But these two are joined together in the answer for these reasons:
1. Because God is pleased to put them together in his Word, under the notion of work and reward. God having put into man in natural desire after happiness or will be, makes use of it to help him in his duty: and therefore having made him for His glory, quickens him to it by a promise of happiness in his so doing. Hence the Scripture is full of such passages wherein the command and promise are connected; Norwood fallen man seek God’s glory had he not this encouragement.
2. Because they are inseparable and practice. A man cannot seek God’s glory aright, but in so doing, he also seeks his own salvation; and this follows from the former. And the conjunction between them in practice is thus stated; namely, God doth, as it were, say to the children of men, “You have a desire to be happy; that you can only be in the enjoyment of me; I am the only adequate object of happiness of the children of men. But if you will truly glorify me, in it you shall be happy. Do you take care of my honor, and I will secure your felicity.” And by this means it comes to pass that all the rules which God gives man to glorify him become through the strong connection sure guide of man to eternal glory. Hence that forementioned Isaiah 56:2; James 1:25. Happiness is made the reward of true obedience, and yet because man does God service, by a tie of nature antecedent to the reward, he is to seek God’s glory, though there were none: so that respect to his own benefit is but a secondary consideration.
Here therefore that great case which some perplexed themselves and others is easily resolved, namely, whether a man ought willingly to be damned, so God’s glory may be advanced by it?
Answer: A willingness to be damned is inconsistent with a true desire that God may be glorified because it separates those things which God has made inseparable. It supposes a clashing in that very order which God hath put between the end and the means: it must therefore presume a consent that God should be false to his word and promise, which militates against his glory; or else a willingness to the neglect the duties to which the promises made; which is to consent to our own actual dishonoring of him; neither of which are consistent with our sincere aiming at our last end.
There are indeed to Scripture examples that seem to make for the contrary conclusion; that of Moses, Exodus 32:32, and of Paul, Romans 9:3. But if thoroughly weighed they will not evince it. Both of them are of one tenor, and neither looks immediately to the glory of God, but to express an exuberant affection to their people. Neither of them in their extent are justifiable. God himself seems to testify against, and tacitly to reprove that of Moses, verse 33, and Paul expresses himself in the potential mood, “I could wish…” I.e. “I have such an endeared love to my kindred, that I am at the point of so wishing; I could do it, if it were lawful.” It is a pathetic all expression of an hyperbolical affection. It must needs therefore be in ensnaring trial that is put upon the children of God, when this is offered as a rule to prove their sincerity by. He that insatiably desires to be saved, and yet resolves to be saved in no other way but that wherein God may be glorified, certainly is the man whose hands are rightly fixed.
From: Sermon 2, Compleat Body of Divinity, In 250 Lectures on the Assembly's Shorter Catechism (published posthumously in 1726), by Samuel Willard (January 31, 1640 – September 12, 1707)