The third cause is to develop the resolve of bodhichitta.
All sentient beings, who are as limitless as space and who have all been our mothers at some point in the past, have fallen into suffering. They don’t even recognize it as suffering but confuse it with happiness.
They are overpowered by karma and the afflictions. Realizing this, we think, “I need to practice in order to help these beings.” That is bodhichitta, the third cause.
Source: Khenchen Thrangu. Advice from a Yogi: An Explanation of a Tibetan Classic on What Is Most Important. Padampa Sangye’s One Hundred Verses. Boston, MA: Shambhala Publications, 2015.
The third principal meditation to cultivate as a condition necessary for rebirth in Sukhavati is to develop the mind of enlightenment, or bodhichitta.
Tulku Thondup says, “You must vow or be determined to lead all mother-beings, without exception, to the Blissful Pure Land without any selfishness, and you must put that aspiration into practice through meditation and beneficial deeds.” [Tulku Thondup, Peaceful Death Joyful Rebirth]
Source: Holecek, Andrew. Preparing to Die: Practical Advice and Spiritual Wisdom from the Tibetan Buddhist Tradition. Boston & London: Snow Lion, 2013.
Bodhicitta (Sanskrit): the “thought of Enlightenment”, or determination to attain Enlightenment for the benefit of sentient beings.
(Geshe Rabten, The Essential Nectar: Meditations on the Buddhist Path)