This comment may allude to an old debate about religion – do you have to believe before you observe, or can you observe without yet believing?
The answer one can see in the Sifre is that through beginning to observe, you come to believe.
Abraham Joshua Heschel makes a similar point when he says there are three ways to God – you sense the presence of God in the world; in the Bible and history; and in sacred deeds. Sacred deeds is the observance of the commandments.
You have to start somewhere; the Jewish way is not so much a leap of faith as a leap of action. Start keeping the mitzvot and you find that your understanding grows and your faith deepens.