Exodus 23 has some interesting glimpses into what the religion of Israel was before the reformers got hold of it.
Exodus 23:14-17 sets out the requirement that three times a year the men of Israel went to the temple. Even as the KJV translates it, the fact that they appear in the presence of the Lord three times a year is interesting. But since "presence" is literally pen, "face," and "appear" could also be read "see," there's an even more provocative possibility: that three times a year, the men of Israel saw the face of the Lord.
Exodus 23:25 is also very suggestive. To "serve" here is 'avadtem, meaning worship in liturgy, perform ordinances. What ordinance is it? It appears to be an ordinance in which the Lord will bless the people's bread and water (cf. Matthew 6). The LXX here adds "wine," suggesting that the Greek-speaking Jews of Alexandria knew that this was a specific ordinance being referred to, and that ordinance, as they knew it, was a feast of bread and wine.