What other nation is like this one, that understands the personality of its God!
…The accepted custom of one who faces judgement is to wear black, to wrap himself in mourning, neglect his hair and fingernails – for he dreads the unknown results of the judgement.
But not Yisrael! They wear white, wrap themselves in white, groom their hair and fingernails, eat and drink and rejoice on Rosh haShana, knowing that the Holy One will perform a miracle for them… (Tur, Orach Chayim 581 [from Midrash])
Then why not wear embroidered and colorful clothing?
…That might imply that he does not fear the Day of Judgement at all and is insensitive, but wearing white demonstrates awareness of the day of death… (Maharshal)
The Torah portrays Avraham returning from the mizbayach alone:
And Avraham returned to his servants and…to Be’er Sheva… (B’reishis 22:19)
for in every sense but the entirely physical, Yitzchak remained behind, a sacrifice burned on the altar:
When they returned from Babylonia…how did they know the precise location [to rebuild] the mizbayach?
They saw the ashes of Yitzchak lying on that spot. (Zevachim 62a)
…the Akeida is much more than a repository of merit. In experiencing the total questioning of Din on Rosh haShana, we relive the Akeida.
I will account it for you as if you had brought yourselves before Me as an akeida. (Rosh haShana 16a)
(Matis Weinberg, Patterns in Time)