William Burkitt on 1 Thessalonians 5:24

Here our apostle comforts the Thessalonians with the assurance that God, who had called them to the knowledge of Christianity, would do what he had prayed for, namely, sanctify them wholly, and preserve them blameless, and this because God is faithful, that is, always the same, true to his word. God will certainly do his part in and towards the work of sanctification and preservation; but in a way of concurrence with our care and industry; he will do nothing without us, as we can do nothing without him; God's faithfulness is a pledge to us of the performance of all his promises, and will most certainly put him upon the performance of them; but his promise to us always supposes, yea, exacts from us, the use of all means, and particularly the exerting of our own endeavours, in order to our preservation in grace, and perseverance in holiness; Faithful is he that called you, who also will do it.