Thomas Brooks emphasizes the importance of a holy heart that perseveres in faith despite external challenges. He identifies three key elements that support this perseverance: divine love as a powerful principle, the Spirit of God as a mighty aid, and the glory of God as a high aim. In contrast, those who only display a facade of godliness are easily swayed by the loss of worldly encouragements and are quick to abandon their faith when they cannot gain from it. Brooks warns that such individuals are like Demas, who forsook his faith for worldly gain, highlighting the dangers of seeking profit and applause over true devotion.