Del ár. hisp. law šá lláh 'si Dios quiere'.
interj.Denota vivo deseo de que suceda algo.
Ojalá comes from the Arabic if God wants it or God-willing but is now defined without reference to a divine figure.
Is it now entirely secular or does it still carry a divine connotation? When someone reads or hears the word do they still read or hear a religious aspect? Would a non-religious person use the word seriously?
Some English corollaries:
Godwilling - the NOAD definition does not mention God ("used to express the wish that one will be able to do as one intends or that something will happen as planned") but I, as a native English speaker, still very much hear this as a reference to a divine figure and would not use it seriously without religious belief.
Goodbye - like adios it literally means, etymologically, God be with you. It has, however, lost all religious connotations.
Which is more true of ojalá?