Literally, this phrase (found originally in the New Testament of the Vulgata) is translated as "into [the] ages of [the] ages". It's supposed to be an expression of eternity, and it's commonly translated in English as "forever and ever". In Spanish it is much more literal than in English: "por los siglos de los siglos". But neither the Spanish nor the literal translation of the Latin seem to me to explicitly convey the meaning of eternity. In a way, the expression itself doesn't make sense. Why "of ages"? What is "an age of an age"? More clear is in aeternum, which is used at least 223 times in the Vulgata (including in the Old Testament).
Is it possible to make sense of the literal meaning of "in saecula saeculorum"? Or must we be content with some figurative meaning, derived from that intended by the author of the phrase?