The key to persevering as a Christian is not your perseverance with God, but God’s perseverance with you. Endurance in the Christian life is built on the person of Jesus—Immanuel, God with us—not your performance. It’s not about your ever-present faith in God, but God’s ever-present faithfulness to you. Your faith will waver, but God’s faithfulness to you never wavers.
Therefore Christian endurance comes from the Gospel—what God has done for you in Jesus—not from what you have done and will do by buckling down and living the Christian life. The Christian life is lived by God’s action for you and God’s presence with you not what you have done and will do for God.
Your faith through difficult times, your faith to endure, does not increase by working up faith but by rediscovering what God has done in the person and work of Jesus Christ and resting in his promise to never leave you or forsake you no matter what. Perseverance in the faith comes from God’s promised perseverance to always be with you and for you. Therefore your endurance as a Christian is more God sticking with you than you sticking with God.
Eugene Peterson writes,
That “[God] sticks with us” is the reason Christians can look back over a long life crisscrossed with cruelties, unannounced tragedies, unexpected setbacks, sufferings, disappointments, depressions—look back across all that and see it as a road of blessing, and make a song out of what we see. “They’ve kicked me around ever since I was young, but they never could keep me down.” God sticks to his relationship. He establishes a personal relationship with us and stays with it. The central reality for Christians is the personal, unalterable, persevering commitment God makes to us. Perseverance is not the result of our determination, it is the result of God’ s faithfulness. We survive in the way of faith not because we have extraordinary stamina but because God is righteous, because God sticks with us. Christian discipleship is a process of paying more and more attention to God’s righteousness and less and less attention to our own; finding the meaning of our lives not by probing our moods and motives and morals but by believing God’s will and purposes; making a map of the faithfulness of God, not charting the rise and fall of our enthusiasms. It is out of such a reality that we acquire perseverance. (A Long Obedience in the Same Direction, 132-133)