"Object. 2. But how can it stand with God's love and mercy to punish his creature for ever? Our bowels are troubled if we should hear the howling of a dog in a fiery furnace for a small space of time. Now God is love itself, 1 John iv. 8; therefore surely he will not damn his creature to everlasting torments.
Ans. Man is not fit to fix the bounds of God's mercy, but the Lord himself; therefore take these considerations:—
1. God's punishments may stand with his mercy. It is very notable, in one place it is said, Heb. x. 31, 'It is a fearful thing to fall into the hands of the living God;' but in another place it is said, 2 Sam. xxiv. 14, 'I am in a great strait; let us fall now into the hands of the Lord, for his mercies are great.' The one noteth God angry, the other God appeased. When God hath been long upon a treaty of love, patience abused is turned into fury. The one showeth what God is in himself, love, sweetness, mercy; the other, what he is when provoked. The sea in itself is smooth and calm, but when the winds and tempests arise, how dreadfully it roareth. God's attributes must not be set a-quarrelling. He is love and mercy, but he is also just, and true, and holy. If he were not angry for sin, he should not love his justice, make good his truth, manifest his holiness, and so hate himself. If God should pardon all sins, his abhorrency and hatred of sin could not be manifested, and so he would lose the honour of his infinite holiness; therefore in men and angels he would declare his displeasure of it, and no less hatred of the sinner. God saw it best for his own glory to suffer some to sin, and by sin to come to punishment. Therefore do not wallow in thy filthiness, and think that God will be all honey, that mercy wilt bear thee out. He hath said that Hare and drunkards shall have their portion in the lake that burneth with fire and brimstone. If God is merciful, and yet did such things to Christ, certainly he may remain merciful much more, and yet punish thee."
Thomas Manton, Several sermons upon Matthew 25, SERMON XXIV (Works, vol. 10).