Milton uses the metaphor of a stream to express God's power as being both eternal and also amorphous or impossible to truly define. His power is so timeless that for some, it is difficult to trace His power to its original source. God is so old that He- the ultimate ‘source’- no one may ‘tell’ of, or truly have knowledge of. The light, then, may be seen to represent man's view of God- as he can never truly comprehend God or the magnitude of his power, his inferior or imperfect vision of Him is thus manifested in the Light. The Light functions as man's eyes when he is trying to 'look at', or perceive, God. The use of water here further speaks of God's power being as water flowing in a stream, i.e. ever-working and in motion.
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