One of the most erroneous doctrines taught by man is that it is impossible to fall from grace.  We sometimes refer to this as the “once saved, always saved” doctrine.  Those who believe it are Calvinists and refer to it as the “perseverance of the saints,” the “P” in the TULIP acronym representing the five points of Calvinism (Total Depravity, Unconditional Election, Limited Atonement, Irresistible Grace, and Perseverance of the Saints).

That man can fall from grace is seen by the warnings of inspired writers in the New Testament and examples of saints who fell.  For instance, we have Paul’s warning to the saints of Galatia.

Galatians 5:3-4 (KJV 1900)
³ For I testify again to every man that is circumcised, that he is a debtor to do the whole law. ⁴ Christ is become of no effect unto you, whosoever of you are justified by the law; ye are fallen from grace.

Then we have examples of Christians who fell (Ananias and Sapphira (Acts 5:1-10), Simon (Acts 8:5-24),  Hymenaeus and Philetus, as well as those they influenced (2 Timothy 2:17-18), Demas (2 Timothy 4:10), etc.

We must recognize the danger of allowing ourselves to be devoured by the devil.  Paul warned us of the danger of falling.  

1 Corinthians 10:12 (ESV)
¹² Therefore let anyone who thinks that he stands take heed lest he fall.

Peter warned us of the continued attempts of Satan to devour us.

1 Peter 5:8 (ESV)
⁸ Be sober-minded; be watchful. Your adversary the devil prowls around like a roaring lion, seeking someone to devour.

The good news is that while we can fall, we do not have to fall.  God has given us the ability to stand against the fiery darts of the devil and the tools to defeat him.

Jude 24–25 (KJV 1900)
²⁴ Now unto him that is able to keep you from falling, and to present you faultless before the presence of his glory with exceeding joy, ²⁵ to the only wise God our Savior, be glory and majesty, dominion and power, both now and ever. Amen.

1 Peter 1:3-4 (ESV)
³ Blessed be the God and Father of our Lord Jesus Christ! According to his great mercy, he has caused us to be born again to a living hope through the resurrection of Jesus Christ from the dead, ⁴ to an inheritance that is imperishable, undefiled, and unfading, kept in heaven for you,

The power that Peter refers to is the gospel of Christ.  Listen to Paul:

Romans 1:16 (ESV)
¹⁶ For I am not ashamed of the gospel, for it is the power of God for salvation to everyone who believes, to the Jew first and also to the Greek.

The gospel is the totality of New Testament teaching, sometimes referred to as “the faith” (Galatians 1:11, 23).  The word of God is our defense.  Paul called it the “sword of the Spirit,” which we should make sure we are wearing at all times.

Ephesians 6:10-17 (ESV)
¹⁰ Finally, be strong in the Lord and in the strength of his might. ¹¹ Put on the whole armor of God, that you may be able to stand against the schemes of the devil. ¹² For we do not wrestle against flesh and blood, but against the rulers, against the authorities, against the cosmic powers over this present darkness, against the spiritual forces of evil in the heavenly places. ¹³ Therefore take up the whole armor of God, that you may be able to withstand in the evil day, and having done all, to stand firm. ¹⁴ Stand therefore, having fastened on the belt of truth, and having put on the breastplate of righteousness, ¹⁵ and, as shoes for your feet, having put on the readiness given by the gospel of peace. ¹⁶ In all circumstances take up the shield of faith, with which you can extinguish all the flaming darts of the evil one; ¹⁷ and take the helmet of salvation, and the sword of the Spirit, which is the word of God,

We do not have to fall away from God at any point in our lives as Christians, but remaining faithful does not happen by accident.  We all, both babes in Christ and seasoned saints, face trials and temptations from the devil.  It is up to us to take advantage of the tools that God has given us, beginning with the Word of God, and use them daily.  The best way to keep from falling is to grow in the knowledge of God’s Word by studying it regularly.  As long as the Word is firmly planted in our minds, we are protected against the devil’s assaults.

1 John 3:9 (ESV)
⁹ No one born of God makes a practice of sinning, for God’s seed abides in him; and he cannot keep on sinning, because he has been born of God.

The Psalmist taught this same truth years before.

Psalm 119:11 (ESV)
¹¹ I have stored up your word in my heart, that I might not sin against you.

Prayer is another tool that can help us overcome the devil.  Right after Paul exhorts us to put on the whole armor of God, he tells us to pray.

Ephesians 6:18 (ESV)
¹⁸ Praying at all times in the Spirit, with all prayer and supplication. To that end, keep alert with all perseverance, making supplication for all the saints,

God has given us what we need to stand.

2 Peter 1:3 (ESV)
³ His divine power has granted to us all things that pertain to life and godliness, through the knowledge of him who called us to his own glory and excellence,

It is up to us to use what He has given.  Make it your goal to never fall away.  If you do, it is not because you have to, but because you choose to.  We are in God’s hand and no one has to power to pluck us away from Him (John 10:29), but we can let go of Him.  It would be the worst decision we could make.  Let us all make sure we do not do it.