With the advent of the Italian Social Republic, he received from Rome the task of reorganizing the structure of the Catholic Action of Northern Italy.

In 1948, on the occasion of the 80th anniversary of the foundation of Catholic Action, he organized a large youth demonstration in Rome which became known as the famous gathering of the three hundred thousand "Green Basque".

It was at this time that he decided to join the religious congregation of the Little Brothers of Jesus which had been founded by René Voillaume and inspired by Charles de Foucauld.

For ten years, he lived an eremitical life in the Sahara composed of prayer, silence and work, an experience he expressed in Letters from the Desert, as in all the books he would later write.

[1] He returned to Italy in 1965 and settled in Spello, Umbria, where Leonello Radi (a former president of GIAC) managed to have the fraternity of the Little Brothers of the Gospel entrust the former Franciscan convent of San Girolamo, near the cemetery.

Leonello Radi said: "the main activity of Carlo Carretto was the eight hours of prayer a day, I carried him I do not know how many times with my red Beetle, during the trip we talked and, above all, we prayed".

Soon the spirit of initiative of Carretto and the prestige it enjoys opened the community to the reception of those who, believers or not, wished to spend a period of reflection and search for faith lived in prayer, in manual work and in the exchange of experiences.

One notable book of that period was the Small Family Church which provoked controversy in the Catholic world over whether the ideas it expressed align with Christian morality.