This is a phrase that can be understood in many different ways.
Assuming that patterns of small selves are reborn over and over, continually evolving and maturing, then some will awaken earlier in the process than other. The conventional view is that it is desirable to awaken as early as possible.
This view makes sense from a certain perspective, if you see suffering as undesirable and liberation as desirable. This is the small self view.
But there is another way of looking at it, which makes more immediate sense to me.
If a small self pattern awaken early on, there are fewer human experiences for it to draw on, there is less substance available in terms of living the awakening as a full human being. The longer it takes before awakening, the more experiences are accumulated, and the richer and fuller the embodiment can be.
In this way, we can see that the last shall be the first. They are the ones who can embody it in a fuller, richer and more deeply human way.
Another way of looking at it is in terms of approach.
In some cases where there is a deep desire for awakening, the embodiment later on is off in certain ways – especially in terms of arrogance. There may be a sense that “I put all this effort into it, and now see how great I am”.
In other cases, where there may have been a curiosity but not a strong desire, the awakening seems more balanced and level-headed.
My partner is an example of this, as she has been curious about spiritual practice for a while but has never been attached to awakening or drawn to any serious practice. Now, that there is a stable awakening to the Absolute, she is remarkably level-headed about it. She recognizes it as a significant shift, but also as not a big deal. As the awakening and integration unfolds further, it means that she could be in a very good position to help others – without all the extra that comes with many other teachers/guides.
Again, the last shall be the first.