John Gill Commentary Genesis 23:18

"unto Abraham for a possession in the presence of the children of Heth, before all that went in at the gate of his city." — Genesis 23:18 (ASV)

To Abraham for a possession. To be enjoyed by him and his forever, as his own property, purchased by his money: in the presence of the children of Heth; they being witnesses of the bargain, and of the payment of the money by Abraham, and of the surrender of the field to him, for his own use.

before all that entered the gates of his city; not of Abraham's city, for he had none, but of Ephron's city, which was Hebron (Genesis 23:10); these are either the same with the children of Heth, and so the clause is added by way of explanation, and including all the inhabitants of the place; or else different from them, they intending the princes of the people that composed the assembly Abraham addressed, and these the common people, the inhabitants of the place.

Aben Ezra takes them to be the travelers that passed and repassed through the gates of the city: However, the design of the expression is to show in what a public manner this affair was transacted, and that the field was made as firm and as sure to Abraham as it could well be, no writings on such occasion being used so early.