Because the fear and service of God are two separate mitzvot, they are not contingent on each other.
There is a mitzva to fear God and there is also a mitzva to serve Him.
Although these two commandments are connected to each other, failure to fulfill one does not prevent the fulfillment of the other.
Consequently, a person can serve God and fulfill the mitzvot with acceptance of the yoke, and he thereby fulfills the mitzva of “Him you shall serve,” even though he has not yet attained the fear of God.
Rabbi Adin Steinsaltz