VATICAN CITY (CNS) — God acts in history to save his people, at times even testing them, rather than simply making them in a petri dish and saving them “aseptically, in a laboratory,” Pope Francis said.

“If we aren’t clear on this, we will never understand Christmas, we will never understand the incarnation of the Word. Never,” he said Dec. 18 during the early morning Mass in the chapel of his residence.

Throughout history, the pope said, God has chosen special people to lead others to him, people like Abraham, Moses and Elijah. Being chosen, he said, was not always the nicest thing that could happen to a person, because it brought “dark moments, uncomfortable moments, moments that annoyed them.”

Like them, “the Lord bothers us to make history. He often makes us follow paths that we don’t want to follow,” the pope said, according to a Vatican Radio report.

But while different people are chosen at different points in history, he said, the truth remains that God walks with people, challenges them, helps them face their problems and continues to save them through his son.

The day’s Gospel reading from St. Matthew recounts “another difficult moment in the history of salvation,” that of Joseph who discovers that Mary is pregnant, the pope said. “He suffers. He sees the women of the village gossiping in the market.”

At the same time, the pope said, Joseph knows that Mary is a good woman, a godly woman, one incapable of infidelity.

In the difficult moments, he said, the special people chosen by God know they must “take the problem on their shoulders without understanding,” and that is what Joseph does.

The Gospel recounts how an angel appears to Joseph in a dream and explains what has happened. “Perhaps psychoanalysts would say this is a dream prompted by anxiety that needs released — let them say what they want!”

“What did Joseph do? After the dream, he took ‘his wife into his home,'” the pope said. Joseph thought to himself, “‘I don’t understand anything, but the Lord told me this and (the baby) will be like my son.'”

Pope Francis told those at the Mass that Christians always must remember that while God may test people, he also helps them overcome trials and saves them.

“Always remember with trust — even in the worst moments, even in sickness, even when we realize that we must ask for extreme unction because there’s no way out — to say: ‘Lord, history did not begin with me and it will not end with me. You keep going, I’m ready.’ And put yourself in the Lord’s hands,” the pope said.