“And this is the manner after which they were ordained—being called and prepared from the foundation of the world according to the foreknowledge of God, on account of their exceeding faith and good works [remember, this faith and works you demonstrated while you were still in the premortal world]; in the first place being left to choose good or evil; therefore they having chosen good, and exercising exceeding great faith, are called with a holy calling … which was prepared with, and according to, a preparatory redemption for such.” (Alma 13:3.)

Thus, you and your fathers were reserved to be bon at a time and in a place where you could not fail to hear the gospel preached and accept the holy priesthood. Thus, a preparatory redemption was made for you through a priesthood heritage from your fathers and mothers.

Andrew Skinner - Temple Worship

the atonement of Jesus Christ already operated on our behalf in premortality in preparation for our mortal sojoun

If the Atonement was in operation during our premortal existence, then, does that mean sin was to be found during that phase of our existence? It certainly seems possible

Some Additional Thoughts:

The very phrase, “preparatory redemption,” seems to be paradoxical: a redemption implies some sort of completion, while preparatoriness implies a lack of completion. In other words, a “preparatory redemption” would be a completion that is marked with incompletion because it points towards another completion still to come. The word “preparatory” even hints that eventual completion will be of the same general character as the incomplete completion of the present: this redemption is to give way to a fuller, more real redemption eventually. But as soon as the issue is phrased this way, the difficulty disappears, or at least becomes part of a broader scriptural theme: redemption is always granted first in a preparatory manner and eventually in a complete manner. Perhaps the clearest parallel to Alma’s phrase here is Paul’s word to the Ephesians: “ye were sealed with the Holy Spirit of promise, which is the eanest of our inheritance until the redemption of the purchased possession” (see Eph 1:13-14). Paul speaks to the saints of having received a redemption of sorts, but one that is ultimately preparatory, separated from its eventual fulfillment (“redemption”) by a promise, by hope.

This gap between two redemptions (the one promising or pointing towards the other) might well be read in terms of ritual as well: ordinances are dramatic enactments of a redemption still to come. Every ordinance might well be called a “preparatory redemption” in the same sense discussed immediately above. That some sort of ordinance–some sort of dramatic enactment of one’s redemption–is what Alma might be talking about is further suggested (and greatly strengthened) by the fact that this “preparatory redemption” is there described as that according to which and with which a “holy calling” was prepared. The implication seems to be that Alma is speaking of an ordinance that at once dramatically embodies one’s redemption and issues a “holy calling” to the participant. What Latter-day Saints call the endowment might not be far from Alma’s mind.