Any person escaping into the territory from whom labor or Services avully claimed... such fugitive may be lawully reclaimed and convey to the person claiming his or her labor or service as aforesaid.
Fill in the blanks to paraphrase what this is saying:
A slave
who runs
into this territory will
be returned
to their owners

That, in all that tract of country ceded by France to the United States, under the name of Louisiana, which lies north of thirty-six degrees and thirty minutes north latitude, excepting only such part thereof as is included within the limits of the State contemplated by this act, there shall be neither slavery nor involuntary servitude, otherwise than in the punishment of crimes, of the party shall have been duly convicted: Provided, always, That any person escaping into the same, from whom labor or service is lawfully claimed in any State or Territory of the United States, such fugitive may be lawfully reclaimed, and conveyed to the person claiming his or her labor or service, as said before.

Explanation:

to stay where they were until m sent for