"20...you stand by faith. Do not be arrogant, but tremble. 21 For if God did not spare the natural branches, he will not spare you either.
22 Consider therefore the kindness and sternness of God: sternness to those who fell, but kindness to you, provided that you continue in his kindness. Otherwise, you also will be cut off. 23 And if they do not persist in unbelief, they will be grafted in, for God is able to graft them in again." (Romans 11:20-23 NIV)
"...Christ is faithful as the Son over God’s house. And we are his house, if indeed we hold firmly to our confidence and the hope in which we glory." (Hebrews 3:6 NIV)
"12 See to it, brothers and sisters, that none of you has a sinful, unbelieving heart that turns away from the living God. 13 But encourage one another daily, as long as it is called “Today,†so that none of you may be hardened by sin’s deceitfulness. 14 We have come to share in Christ, if indeed we hold our original conviction firmly to the very end." (Hebrews 3:12-14 NIV)
"22...he has reconciled you by Christ’s physical body through death to present you holy in his sight, without blemish and free from accusation— 23 if you continue in your faith, established and firm, and do not move from the hope held out in the gospel." (Colossians 1:22-23 NIV)
"1 Now, brothers and sisters, I want to remind you of the gospel I preached to you, which you received and on which you have taken your stand. 2 By this gospel you are saved, if you hold firmly to the word I preached to you. Otherwise, you have believed in vain." (1 Corinthians 15:1-2 NIV)
Why be careful to not lose a faith you can not lose? Simple question.