Charles Ellicott Commentary 1 Chronicles 29:21

"And they sacrificed sacrifices unto Jehovah, and offered burnt-offerings unto Jehovah, on the morrow after that day, even a thousand bullocks, a thousand rams, and a thousand lambs, with their drink-offerings, and sacrifices in abundance for all Israel," — 1 Chronicles 29:21 (ASV)

On the morrow after that day (lĕmohŏrath hayyôm hahû); here only. (Compare to Jonah 4:7.) That is, on the day after the assembly.

A thousand bullocks ... —Hebrew, Bullocks a thousand, rams a thousand, etc., according to the later mode of speech; and their libations (Psalms 16:4; Exodus 29:40; Leviticus 23:13).

And sacrifices in abundance for all Israel. —The word “sacrifices” (zĕbâhîm) occurred in a general sense at the beginning of the verse. Here, in connection with burnt-offerings, it has the special meaning of “thank-offerings” (shĕlâmîm; Authorized Version, “peace-offerings,”Deuteronomy 12:6). See for both kinds of sacrifice, Leviticus 1:1 and following; Exodus 20:24; Exodus 24:5.

For all Israel. —So that everyone present might partake of the sacrificial meal. (Compare to Notes on 1 Chronicles 16:2–3; Deuteronomy 12:7; 1 Samuel 1:3–8; 1 Samuel 1:13.)