54 The first of them is the spirit of poverty, or rather, the zeal for preserving this spirit. We presume to mention it explicitly in this encyclical letter because of Our conviction of the prominence which this precept receives in Christ's holy Gospel. It is a fundamental element of that divine plan by which we are destined to win the kingdom of God, and yet it is greatly jeopardized by the modern trend to set so much store by wealth. The zeal for the spirit of poverty is vitally necessary if we are to realize the many failures and mistakes we have made in the past, and learn the principle on which we must now base our way of life and how best to proclaim the religion of Christ.
Source: Ecclesiam Suam (Vatican.va)