What is the ruling on not giving lectures to Christians?

If Christians are peaceful towards Muslims, then Islamic law does not prohibit showing kindness and righteousness to them, based on the Almighty's saying: "Allah does not forbid you from those who do not fight you because of religion and do not expel you from your homes - from being righteous toward them and acting justly toward them. Indeed, Allah loves those who act justly." It is permissible to assist them in acts of righteousness and justice that are permissible by religious law.