1 Thessalonians 5:24 (ESV) … “He who calls you is faithful; he will surely do it.”
The follower of Christ is never left alone: The one who calls you is faithful and he will do it. Here is great comfort and assurance. We are never abandoned. God’s faithfulness is the undergirding of our faith. Our hope and trust are placed in a trustworthy God. The call of God is not separated from his faithful enabling. In our struggles we can rest in him.
The promise comes from God himself—the Author of the plan, the One who accomplished it through the death of his Son, the One who calls his people, and the One who cannot lie. “God is not a human being, that he should lie, or a mortal, that he should change his mind. Has he promised, and will he not do it? Has he spoken, and will he not fulfill it?” (Numbers 23:19 nrsv).
Faithfulness is a characteristic of God. God created the world, and he has faithfully ordered it and kept it since the Creation. Because God is faithful, believers can count on him to fulfill his promises to them. If God can oversee the forces of nature, surely he can see his people through the trials they face. Trusting in God’s faithfulness day by day gives confidence in his great promises for the future. What he has promised, he will do.
 Larson, K. (2000). I & II Thessalonians, I & II Timothy, Titus, Philemon (Vol. 9, p. 76). Nashville, TN: Broadman & Holman Publishers.  Barton, B. B., & Osborne, G. R. (1999). 1 & 2 Thessalonians: life application commentary (p. 96). Wheaton, IL: Tyndale House Publishers.