Over Pesach I had the opportunity to read a few modern Jewish philosophy books and I'm still in the process of digesting them. A couple of them really stuck out though. One was by Isaiah Leibowitz and the other by Mordechai Kaplan. Suffice it to say they each had rather different takes on Judaism.
Leibowitz takes the stand as a metaphysical reductionist and what I'd consider to be a Jewish Kierkegaard. In his view God simply exists and the best way of doing Judaism is through following Halacha for the sake of serving God. Doing Halacha for any other purpose, be it for moral reasons, sociological reasons or political reasons is to turn God's Law into service for man and not for God. Thus doing Mitzvot for the sake of reward or fear of punishment is the basest type of religion since it is purely selfish as opposed to the purely selfless ideal of Leibowitz. Thus he criticizes people like Maimonides who seach for rational justifications for the Law. If Halacha is to serve God then its utility to man is irrelevant.
Leibowitz reminds me of Kierkegaard because he has the same idea that faith and service in God is the ultimate objective in life beyond that of any moral concern or ethical imperative. Thus he uses the Akeidah as an example of God's commands overruling any moral conscience. One's ultimate fidelity lies with God and not with anything else.
There are some issues though with Leibowitz. He in other places claims that Judaism is only meaningful in the sense as the "following of Halacha." He says that since Judaism has had many different theologies and religious philosophies over time the only consistent measure to identify Judaism is through those who live a Halachic life. He thuswise tries to make irrelevant all the metaphysical theories behind Judaism and even the imperative behind composing a metaphysical theory to justify it. The problem is that one must make certain assumptions about the relationship between God and Halacha to say that one is serving God by following Halacha. If Halacha is a creation by man and not truly a command from God then one is serving men, not God.
Leibowitz doesn't outrightly say this anywhere in his book, but I suspect that he basically makes the assumption that the Torah is min hashamayim and Halacha is divinely inspired. Though, I think, you don't need to make that assumption. Even if Halacha was and is devised solely by man, one can still serve God in a way that makes sense to man. God is unfathomable and the ultimate reality. For "Him" to command anything is likewise unfathomable and nonsensical. We must rely on human invention to try and relate to "Him." And the best way to serve Him is through doing that which has no utility to man. For if an act has utility to man then its value as a service to God is much reduced if not entirely so.
In this way we can justify all those apparently silly and meaningless rituals in Judaism. Every one of those Chukim are explained thus. One would be absolutely correct in saying that they serve no purpose to man. For if they served man then that would undermine the whole point. The intention is a service to God.
The problem I run in with Leibowitz is that he says that following Halacha supercedes ethical and moral imperatives. Indeed, how can he not? How can the utility to man's needs come before the will of God? But if Halacha is not the will of God, but rather the innovation of man then this solves the problem. For those laws which are ethically or morally neutral then why not do them? They are a service to God and nothing else. But when a law crosses ones conscience then we must hold one's conscience supreme.
Then this is where Kaplan comes into play. Since the God of Leibowitz is transcendent and unknowable, how are we to relate to Him? We cannot. What Kaplan does is to turn what is meaningful for man into that which is God. God is the power that makes for freedom. God is the power that makes for cooperation. God is the power that makes for social regeneration, for salvation and for Righteousness.
God is that which is virtuous and strived for in human nature. God is morality. For God to come before moral imperatives is impossible. God is the moral imperative. To honestly follow one's conscience is to walk in the ways of the Lord.