Note: アマテラス大神, 蘇神, 筆神, and 天の川 are proper names, you may just disregard those.
As always this is a quote from a game and the context is that the main character is the reincarnation of a god on a quest to regain her former powers she has lost. This quote is from one of the gods giving you back on of these powers, i.e. rejuvenation. Giving the translation a quick (and rough) whirl, this is what I came up with:
Oh, our great Mother Amaterasu
Just how much time has passed since you've left this world.
And despite that I have been waiting for this very day without fail.
The thirteen gods of the brush have gotten lost all over this mortal world the moment you disappeared.
I have turned into a constellation in order to survive but shall once more serve you and give you the power of rejuvenation.
With this power you shall be able to fill the river of the heavens in an instant.
I'm not that well-versed in old Japanese so please excuse the shoddy translation leaving out any possible nuances. What I'm actually interested here is the usage of ～させ給う as I've come across that more than in just one instance.
Going by my first intuition, I would have said that 仕わせ (I assume the 給え here is dropped as it appears after the second verb in the sentence anyway) and 見継がせ給え mean something akin to 'allow me to serve you' and 'allow me to help you' respectively (with the させ給え meaning …をおさせになさって; or maybe just simply ～させてください?) while 溢れさせ給いぬ means 'surely you shall be able to fill...' (in this case 給う meaning お…なさる) or something similar.
I got the info on ～させ給う from this site by the way; maybe I have misinterpreted the definitions, so if I have gotten anything wrong, please let me know!