Definition:
Sustaining grace refers to the divine assistance and support that God provides to believers, enabling them to persevere in faith and righteousness throughout their lives. It is the grace that upholds Christians in their daily walk, empowering them to endure trials, resist temptation, and grow in spiritual maturity.

Biblical Foundation:
Sustaining grace is rooted in the character of God as a loving and faithful provider. The Bible presents numerous instances where God's grace is depicted as a sustaining force for His people.

1. God's Promise of Sustenance:
In 2 Corinthians 12:9, the Apostle Paul recounts the Lord's assurance to him: "But He said to me, 'My grace is sufficient for you, for My power is perfected in weakness.'" This verse highlights the sufficiency of God's grace in sustaining believers, especially in times of weakness and trial.

2. Daily Provision:
The Lord's Prayer, as recorded in Matthew 6:11, includes the petition, "Give us this day our daily bread." This request underscores the believer's reliance on God's daily provision, both physically and spiritually, as an expression of His sustaining grace.

3. Endurance in Trials:
James 1:2-4 encourages believers to "consider it pure joy, my brothers, when you encounter trials of many kinds, because you know that the testing of your faith develops perseverance." Sustaining grace is evident in the way God uses trials to strengthen and mature the faith of His people.

4. Perseverance in Faith:
Philippians 1:6 assures believers of God's ongoing work in their lives: "being confident of this, that He who began a good work in you will continue to perfect it until the day of Christ Jesus." This verse reflects the sustaining grace that ensures the completion of God's work in the believer's life.

5. Strength in Weakness:
Isaiah 40:29-31 speaks of God's provision of strength to the weary: "He gives power to the faint and increases the strength of the weak. Even youths grow tired and weary, and young men stumble and fall; but those who wait upon the LORD will renew their strength." This passage illustrates the sustaining grace that renews and empowers believers.

Theological Implications:
Sustaining grace is a testament to God's ongoing involvement in the lives of His people. It emphasizes the believer's dependence on God for spiritual vitality and growth. This grace is not earned but is a gift from God, reflecting His unmerited favor and love.

Practical Application:
Believers are encouraged to rely on God's sustaining grace through prayer, scripture reading, and fellowship with other Christians. Recognizing their own limitations, they are to seek God's strength and guidance in all aspects of life. Sustaining grace calls for a life of gratitude, humility, and trust in God's provision and timing.

Conclusion:
While sustaining grace is a continuous theme throughout the Bible, it is most profoundly experienced in the daily lives of believers who trust in God's promises and rely on His strength. It is a vital aspect of the Christian journey, ensuring that believers are upheld and empowered to live out their faith in a fallen world.