What Are [The] Three Obstacles?
Those three obstacles [are] thus  afflictions’ obstacles,  karmic obstacles [and]  retribution’s obstacles.
 Afflictions [are] thus ignorance, also named as confusions. Thus are [those] with principles not understood, (thus [with] greed, anger [and] ignorance), falsely giving rise [to] all kinds of thoughts [that do] not accord [with] principles.
[Note 1: Ignorance (无明/愚痴) is also named as delusion. When the principles (理) of the Dharma (i.e. reality or truth) are not understood, there will be ignorance, from which greed (贪) and anger (嗔) arise.]
([If] desiring [to] eliminate all kinds of thoughts [that do] not accord [with] principles, [this] first needs understanding [that the] world’s all dharmas, are all [with] suffering, are emptiness, are impermanent, are non-self, [and] are not pure. Then [will the] three poisons [of] greed, anger [and] ignorance, [be] unable [to] then arise. See Third Compilation’s Letter For Xiè Róngtuō.)
[Note 2: Dharmas (法) are phenomena of mind and matter (身心). As all phenomena is impermanent (无常), it is non-self (无我) (i.e. without self), with emptiness (空) in terms of being empty of permanence (常) and self (我). Thus, clinging to phenomena as otherwise will give rise to suffering (苦). Thus is such phenomena not pure (不净).]
 Karmas [are] thus due [to the] mind of  afflictions [from] greed, anger [and] ignorance, [with] those doing evil matters of killing, stealing, sexual misconduct [and] others, thus named as karmas.
[Note 3: The karmas (业) above are evil karmas (恶业) as they arise from the three poisons (三毒). These three poisons are also the root causes of the three obstacles (三障).]
[With] these  karmas already accomplished, then [in the] future, [they] definitely must [be] received [with the] three realms’ evil  retribution, of hell-beings, hungry ghosts [and] animals.
[Note 4: The realm of hell-beings (地狱众生) is predominantly with anger (or hatred: 嗔), the realm of hungry ghosts (饿鬼) is predominantly with greed (贪), and the realm of animals (畜生) is predominantly with ignorance (痴).]
[Note 5: To summarise,  afflictions’ obstacles are (pre-existing or) ‘past’ hindrances (already present) (that create suffering),  karmic obstacles are present hindrances (that create suffering), and  retribution’s obstacles are future hindrances (that create suffering).]
[Note 6: As taught by Śākyamuni Buddha (释迦牟尼佛) in Meditation’s Secret Essential Methods’ Sūtra《禅秘要法经》, ‘You and others should teach those future sentient beings [i.e. those who surely include us in this Dharma-Ending Age] with transgressive karmas many, for eliminating transgressions thus, teach to enable them to be mindful of Buddha. With mindfulness of Buddha thus, eliminate all karmic obstacles, retribution’s obstacles and afflictions’ obstacles.’ (汝等当教未来众生罪业多者，为除罪故，教使念佛。以念佛故，除诸业障、报障、烦恼障。)]
Pure Land Tradition’s 13th Patriarch Great Master Yìnguāng
Dharma Master Yìnguāng’s Collected Writings (Third Compilation): Reply Letter [To] Níng Déjìn;
Record [Of] Great Master Yìnguāng’s Collected Writings’ Essence (106th Short Section): 3rd [Chapter]: Guidance [On] Practice Methods: Third, Clear Remedies [For] Habitual Tendencies (13th Short Section)
[Ref: #106 / 3.3.13]
Namo Amituofo : Translation and notes by Shen Shi’an
Record Of Great Master Yìnguāng’s Collected Writings’ Essence