Based on Chapter 38, what are the prescribed means of spiritual progress for each of the four ages (Yugas), and which is most important now?

Chapter 38 provides a clear hierarchy of spiritual practices corresponding to the different cosmic ages, or Yugas. It follows the scriptural assertion that the primary means of spiritual advancement changes with time. According to the information in Chapter 38, Penance (Tapas) was the proven means in the Krita age, Knowledge (Jnana) was key in the Treta age, and Sacrifice (Yajna) was central in the Dvapara age. For the current age, the Kali age, the text explicitly states that Charity (Dan) is the most effective and important practice. The chapter goes on to specify that among all forms of charity, the donation of food (Annadan) is the foremost and highest secret for spiritual merit in our time.