VATICAN CITY — Caring for migrants and the poor is as holy a pursuit as opposing abortion, Pope Francis declared in a major document issued by the Vatican on Monday morning.

Pushing back against conservative critics within the church who argue that the 81-year-old pope’s focus on social issues has led him to lose sight of the true doctrine, Pope Francis again cast himself, and the mission of the Roman Catholic Church, in a more progressive light.

“The other harmful ideological error is found in those who find suspect the social engagement of others, seeing it as superficial, worldly, secular, materialist, communist or populist,” Pope Francis wrote in an apostolic exhortation on the subject of holiness issued Monday morning. “Our defense of the innocent unborn, for example, needs to be clear, firm and passionate. Equally sacred, however, are the lives of the poor, those already born, the destitute, the abandoned.”

The pope’s vision of holiness explicitly highlights migrants, whose plight he has sought to elevate to global attention perhaps more than any other issue.