persevere, perseverance

Definition

To persevere means to continue in a belief or a task even though it may take a long time or be very difficult.

To persevere can also mean to keep acting in a Christ-like way even while going through difficult trials or circumstances.
Perseverance is the character quality that enables a person to keep doing what they should do, even when it is very difficult.
Be careful not to use a word like "stubborn" which usually has a negative meaning.