Is it permissible to say to non-Muslims that Muslims, Christians, and Jews worship one God, with the difference that Muslims affirm God’s oneness while Jews and Christians associate partners with Him? Is this statement correct? Do Jews and Christians worship the God that Muslims worship, but associate partners with Him, and is this the reason for their disbelief?

If you mean that the true God of Muslims, Christians, and Jews is one God, who is Allah the Almighty, then this is correct, as Allah the Almighty says: "And say, "We have believed in that which was revealed to us and revealed to you, and our God and your God is one, and we are in submission to Him." [Al-Ankabut: 46]. The God Whom we worship and Whom they worship is one, having no partner in His divinity, Lordship, names, and attributes. However, we affirm His oneness, while they associate partners with Him. The disbelief of Jews and Christians is not only due to their polytheism but also because of their denial of the message of Muhammad, peace be upon him. So, whoever does not believe in him is a disbeliever, even if he does not assert the Trinity or that Uzayr is the son of God. The reason for the misguidance of Jews and Christians is their failure to follow the teachings of their books, which call to monotheism.