Worshipping together as a community, in the broadest sense of the term “worship,” requires mutual agreement on certain basic principles, such as the nature of the worship and its object. Without minimal uniformity of belief and purpose, people are unable to join together in their sacred tasks. One of those beliefs necessary for a religious community is belief in God, the object of worship. But what should someone unable to assent to that belief do? What does Judaism require of those who do not believe in God?
The question is only partly comprehensible. If someone does not believe in God, why would he care what God demands of him? However, there are degrees of belief and disbelief, and people often fluctuate within that spectrum. Belief is not a yes-or-no proposition but a cycle of varying strengths. Someone who is currently at the bottom of the scale may gain more confidence in his faith in a week, a month or a decade when his experiences and both emotional and intellectual moods have changed. Even someone who seemingly does not believe may want to believe or may be lack certainty in his disbelief. He might want to fulfill whatever religious obligation he can, whether out of caution, desire, habit or deference to another person.
The Rambam (Sefer Ha-Mitzvos, aseih 1; Mishneh Torah, Hilkhos Yesodei Ha-Torah 1:1) lists belief in God as a positive commandment. Others disagree, questioning the circularity of a command to believe in a Commander and the lack of free will in matters of faith. With this second question, the dissenters assert that a commandment implies a choice. Since people cannot choose what to believe, they cannot be commanded to believe.
R. Chasdai Crescas (Or Hashem 2:5:5) proposes a different definition of this commandment. The obligation is not to believe but to try to believe and, if unable, to be disappointed. These are acts and attitudes you can choose to adopt, even if you ultimately fail to achieve complete faith. Others suggest that this was Rambam’s real intent (see Kinas Sofrim to Sefer Ha-Mitzvos, aseih 1; R. Yitzchak Abarbanel, Rosh Amanah, ch. 11 intro. 9).
According to these thinkers, Jews are commanded to try to believe in God. Those blessed with the gift of faith can easily fulfill this commandment, finding God with little intellectual and emotional effort. But such people are still challenged to sustain this belief throughout their lives, despite whatever tragedies they may witness and whatever misfortunes may befall them. No one may believe in himself, in his unwavering faith, because he cannot know what challenges his faith may yet face.
Those unable to believe are still obligated to struggle with faith, to search for answers and attempt to find God. This is every person’s lifelong journey, with its ups and downs of faith. As long as you continue trying, patiently thinking, feeling and exploring, you have done your part, fulfilling the mitzvah of searching for belief in God. Ceasing to argue, stopping to care, giving up on God — that is the real sin.