Most Jews tend to identify Maimonides, Saadia Gaon, Judah HaLevi, Martin Buber as among the great Jewish philosophers of all time, but there are a number of ancient Jewish thinkers whose ideas are rich with originality; in fact, their insights are no less valuable today than they were over two thousand years when they first introduced their wisdom to the world.
Among those scholars we are quoting, we will cite the Wisdom of Ben Sira, who is better known by his Greek name, Sirach. Sirach’s perspective on many philosophical themes continue to delight moderns, and I am glad to consider myself among his followers. Ben Sira lived about 2200 years ago and his book almost made it into the Bible, but fell a little short of the mark. I imagine that the conservatives of Late Antiquity probably felt a little threatened by Sira’s novel way of looking at Judaic wisdom. In modern terms, Ben Sira never worried about “political correctness.” His straight-forward style of writing puts him in a class all of his own.
The second thinker we shall examine is Philo of Alexandria, who arguably is considered the founder of medieval theology. He is the first Jewish thinker to fully integrate Judaic and Greek thought. He flourished in Alexandria, a city that rivaled even Athens when it came to wisdom. Founded by Jewish settlers who admired Alexander the Great. Alexandria soon produced the world’s first university. Philo would have disappeared from Jewish history had it not been for the Early Church Fathers who admired his exegetical style and originality. Had Maimonides been familiar with Philo’s writings, he would have quoted him profusely.
Here is one example how the ancient Jewish thinkers briefly dealt with the issue, “On the Limits of Human Knowledge.”
Ben Sira says, “What is too sublime for you, seek not, into things beyond your strength search not. What is committed to you, attend to; for what is hidden is not your concern. With what is too much for you meddle not, when shown things beyond human understanding. Their own opinion has misled many, and false reasoning unbalanced their judgment. Where the pupil of the eye is missing, there can be no light; and where there is no knowledge, there is no wisdom” (Sirach 3:19-24).
Philo says, “For it does not say that the wise man saw God but that God appeared to the wise man; for it was impossible for anyone to comprehend by his own unassisted power the true living God, unless he himself displayed and revealed himself to him” (On Abraham, 4).
In general, the Sages disliked the speculative thinking of Greek thought and culture. The Sages’ reticence to embrace philosophical wisdom were reinforced by the tragic experiences of the famous four teachers who had studied the ultimate mysteries: Akiba, Ben Azzai, Ben Zoma and Elisha ben Abuyah. A cryptic passage tells of their fate: “Ben Azzai gazed and died; Ben Zoma gazed and became demented; Acher (Elisha) cut the plants (turned apostate); R. Akiba departed in peace.”  As to what exactly happened to these men, we will leave aside for another discussion.
Interestingly enough, Rabbi Akiba is considered by some modern scholars to be among the early founders of Jewish mysticism. Mysticism often propels its followers to abandon the material world but in R. Akiba’s case, we can discover the mystical realm through our ordinary interactions; the world is full of mystical expression and meaning–all we have to do is to pay attention to the synchronicity of events that unfold in our lives daily.
The assertion that God is invisible made Him seem unreal for people who were accustomed to identify reality with concreteness. The rabbis often felt that the human mind could barely grasp the existence of God’s Reality, but could never comprehend the nature of God’s essential nature. Thus it is related in a Talmudic anecdote that the Emperor Hadrian had said to Rabbi Joshua ben Hananiah: “I desire to behold your God.” Rabbi Joshua explained to him that it was impossible. Still and all, the Emperor persisted. Finally, the rabbi relented and asked him to stand in a fixed gaze at the sun. The Emperor found the sun’s light too strong to behold. Triumphantly, the rabbi exclaimed: “If you admit that you are unable to look at the sun, which is only one of the ministering servants of the Holy Blessed One, how can you honestly expect to behold God, Whose existence is even more dazzling?” For some of the Sages, the reality of God by analogy to the soul whose specific abode we do not know and of which we have no direct concrete experience. That, however, does not make it unreal. 
 BT Hagiga 14b, Zohar I, 26b.
 BT Hullin 59b; Midrash Tehillim, Psa. 103:1.