The Life Here Spoken of is the Higher Life, that of Reason
As for those who make up a mythology about the æons and arrange them in syzygies (yokes or pairs), and who consider the Logos and Life to have been emitted by Intellect and Truth, it may not be beside the point to state the following difficulties. How can life, in their system, the yokefellow of the Word, derive his origin from his yokefellow? For “what was made in Him,” he says, evidently referring to the Word, mentioned immediately before, “was life.” Will they tell us how life, the yokefellow, as they say, of the Word, came into being in the Word, and how life rather than the Word is the light of men.
It would be quite natural if men of reasonable minds, who are perplexed with such questions and find the point we have raised hard to dispose of, should turn round upon us and invite us to discuss the reason why it is not the Word that is said to be the light of men, but life which originated in the Word. To such an enquiry we shall reply that the life here spoken of is not that which is common to rational beings and to beings without reason, but that life which is added to us upon the completion of reason in us, our share in that life, being derived from the first reason (Logos).
It is when we turn away from the life which is life in appearance only, not in truth, and when we yearn to be filled with the true life, that we are made partakers of it, and when it has arisen in us it becomes the foundation of the light of the higher knowledge (gnosis). With some it may be that this life is only potentially and not actually light, with those who do not strive to search out the things of the higher knowledge, while with others it is actually light. With these it clearly is so who act on Paul's injunction, “Seek earnestly the best gifts;” and among the greatest gifts is that which all are enjoined to seek, namely, the word of wisdom, and it is followed by the word of knowledge.
This wisdom and this knowledge lie side by side; into the difference between them this is not a fitting occasion to enquire.
Source: Commentary on the Gospel of John (New Advent)