Matthew 24:13 is a simple statement that there are struggles and trials. This text is stated in the context of the destruction of Jerusalem in particular, and it is an exhortation to persevere.
When someone is given an exhortation, it does not mean there is necessarily a doubt as to their future destiny. Rather, it’s an encouragement to keep on going to the future destiny. So, if you’re a father with small children and you say, “Hurry up,” you’re not doubting that they’re going to get to the destination; you are giving them an exhortation to fit into the way that you get to the destination.
Because there are many dangers, toils, and snares in the world through which we have to come, we need these exhortations, and the New Testament is full of them. They need to be put in the context of statements like Jesus saying, “If anyone comes to Me, I will never cast him out,” and, “I have not lost anyone that the Father has given to Me.”
So, these two things go together: the assurance of God’s hand upon us and the fact that God wants us to persevere to keep on living and growing in the Christian life. These are not exhortations to fear but exhortations to encourage us to obey.