Abu Hurairah relates that the Messenger of Allah ﷺsaid: “A person who calls people towards doing good deeds will get the same reward as those who follow him and do good; and nothing will be diminished from the requital of the latter. Similarly, those who call the people towards vice will have the same punishment as those who follow him without any diminution in the punishment of the perpetrators.”
(Sahih Muslim)
This hadīth gives good tidings to one who invites people to virtue, and warns him against inviting others to vice. Calling people towards doing good deeds is in itself a virtuous act. It wins the pleasure of the Lord Almighty. Contrary to it, the act of inviting people to commit some evil is a vicious act. It earns Divine wrath.
God can give reward and likewise award punishment, here on earth and in the hereafter as well, to whom He wills. But this does not mean that His judgement is baseless. He knows perfectly well the deeds done by His servants as well as the intent lurking behind the commission of the deeds. Hence His judgement is based on human actions. He however can forgive whomsoever He wills.
The present hadīth encourages the believer to call people towards doing good deeds because it will earn the same reward for him as those who in response to his call do good deeds. Similarly, it forbids him to invite people to do evil because it is a sin and earns the same punishment.