And Joshua said unto the people, Ye cannot serve the LORD: for he is an holy God; he is a jealous God; he will not forgive your transgressions nor your sins.

Wesley's Notes

24:19 Ye cannot - He speaks not of an absolute impossibility, (for then both his resolution to serve God himself, and his exhortation to them had been vain) but of a moral impossibility, or a very great difficulty, which he alledgeth not to discourage them from God's service, but to make them more considerate in obliging themselves; and more resolved in answering their obligations. The meaning is, God's service is not, as you seem to fancy, a slight and easy thing, but it is a work of great difficulty, and requires great care, and courage and resolution; and when I consider the infinite purity of God, that he will not be mocked or abused; and withal your proneness to superstition and idolatry, even during the life of Moses, and in some of you, while I live, and while the obligations which God had laid upon you in this land, are fresh in remembrance; I cannot but fear that after my decease you will think the service of God burdensome, and therefore will cast it off and revolt from him, if you do not carefully avoid all occasions of idolatry. A jealous God - In the Hebrew, He is the holy Gods, holy Father, holy Son, holy Spirit. He will not endure a partner in his worship; you can not serve him and idols together. Will not forgive - If you who own yourselves his people and servants, shall wilfully transgress his laws, he will not let this go unpunished in you, as he doth in other nations; therefore consider what you do, when you take the Lord for your God; weigh your advantages and inconveniences together; for as if you be sincere and faithful in God's service, you will have admirable benefits by it; so if you be false to your professions, and forsake him whom you have so solemnly avouched to be your God, he will deal more severely with you than with any people in the world.

King James Translators' Notes

holy God: Heb. holy Gods

Matthew Henry's Concise Commentary

24:15-28 It is essential that the service of God's people be performed with a willing mind. For LOVE is the only genuine principle whence all acceptable service of God can spring. The Father seeks only such to worship him, as worship him in spirit and in truth. The carnal mind of man is enmity against God, therefore, is not capable of such spiritual worship. Hence the necessity of being born again. But numbers rest in mere forms, as tasks imposed upon them. Joshua puts them to their choice; but not as if it were indifferent whether they served God or not. Choose you whom ye will serve, now the matter is laid plainly before you. He resolves to do this, whatever others did. Those that are bound for heaven, must be willing to swim against the stream. They must not do as the most do, but as the best do. And no one can behave himself as he ought in any station, who does not deeply consider his religious duties in family relations. The Israelites agree with Joshua, being influenced by the example of a man who had been so great a blessing to them; We also will serve the Lord. See how much good great men do, by their influence, if zealous in religion. Joshua brings them to express full purpose of heart to cleave to the Lord. They must come off from all confidence in their own sufficiency, else their purposes would be in vain. The service of God being made their deliberate choice, Joshua binds them to it by a solemn covenant. He set up a monument of it. In this affecting manner Joshua took his last leave of them; if they perished, their blood would be upon their own heads. Though the house of God, the Lord's table, and even the walls and trees before which we have uttered our solemn purposes of serving him, would bear witness against us if we deny him, yet we may trust in him, that he will put his fear into our hearts, that we shall not depart from him. God alone can give grace, yet he blesses our endeavours to engage men to his service.