If anyone swears by a religion other than Islam falsely and intentionally, he is as he has said

Thābit ibn Ad-Dahhāk al-Ansāri (may Allah be pleased with him) is one of those who gave an oath of allegiance to the Prophet (may Allah's peace and blessings be upon him) under the tree in Bay‘at Ar-Ridwān on the day of Hudaybiyah. He reported that the Prophet (may Allah's peace and blessings be upon him) said that if someone intentionally swears by a religion other than Islam, he would be as he swore.

In other words, he would be a Jew, Christian, Zoroastrian, or a disbeliever, or he would be disassociated from Allah and His Messenger if did such and such. If he falsely makes such an oath intentionally, he would belong to the non-Islamic religion that he had ascribed himself to in the oath. And if someone kills himself with a sword, knife, bullet, or any lethal object, he will be punished with that object on the Day of Judgment.

Additionally, if a person makes a vow on something that he doesn't possess, like vowing to free a slave that he does not own or to give charity from someone else's money, such a vow is null and void, because the one making the vow doesn't own what he is making the vow on. Also, cursing a believer is like killing him, because both acts violate what Allah, the Almighty, has prohibited and are considered as sins and warrant a punishment.

Furthermore, if someone exaggerates and proudly claims to have what he does not possess, such as wealth, knowledge, family background, position, etc., Allah will increase him in nothing but humiliation and degradation. This is because such a person wants to elevate himself through something he doesn't have. So, he will be punished with the opposite of his objective.