The basic principle of brahminical culture is to satisfy Lord Viṣṇu, the personification of sacrificial and ritualistic ceremonies. Lord Viṣṇu is the personified reservoir of all religious principles, and He is the shelter of all the demigods, the great pitās, and the people in general. When the brāhmaṇas are killed, no one will exist to encourage the kṣatriyas to perform yajñas, and thus the demigods, not being appeased by yajña, will automatically die.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
विष्णुर्द्विजक्रियामूलो यज्ञो धर्ममयः पुमान् । देवर्षिपितृभूतानां धर्मस्य च परायणम्
viṣṇurdvijakriyāmūlo yajño dharmamayaḥ pumān | devarṣipitṛbhūtānāṃ dharmasya ca parāyaṇam
SB 7.2.11