en_tn/rom/08/21.md

in the certain hope that the creation itself will be delivered

You can translate this in an active form. AT: "Because God knew that he would save creation" (See: rc://en/ta/man/translate/figs-activepassive)

from slavery to decay

Here being in slavery to decay is a metaphor for being certain to decay. AT: "from being like a slave to decay" (See: rc://en/ta/man/translate/figs-metaphor)

that it will be brought into the freedom of the glory of the children of God

"Freedom" here is in contrast with slavery to decay. It is a metaphor meaning that the creation will not decay. AT: "that it will become gloriously free from decay like the children of God" (See: rc://en/ta/man/translate/figs-metaphor)