I don't agree with OSAS, however I don't believe born again believers will fall away. I don't think they can because they have the Holy Spirit in them.
Mathew 7:24-27 talk about building your house on a rock. This means building your faith so that it will withstand unbelief. The only way to do this is to become born again. Once regeneration begins, it cannot become undone.
Matthew 7:21-27 is about living in compliance of Jesus’ instructions.
“"Not everyone who says to Me, 'Lord, Lord,' will enter the kingdom of heaven,
but he who does the will of My Father who is in heaven will enter. Many will say to Me on that day, 'Lord, Lord, did we not prophesy in Your name, and in Your name cast out demons, and in Your name perform many miracles?' And then I will declare to them, 'I never knew you;
DEPART FROM ME, YOU WHO PRACTICE LAWLESSNESS.' "Therefore
everyone who hears these words of Mine and acts on them, may be compared to a wise man who built his house on the rock. And the rain fell, and the floods came, and the winds blew and slammed against that house; and yet it did not fall, for it had been founded on the rock.
Everyone who hears these words of Mine and does not act on them, will be like a foolish man who built his house on the sand. The rain fell, and the floods came, and the winds blew and slammed against that house; and it fell-and great was its fall."”
Matthew 7:21-27 NASB
At the end of Ephesians 4 on into the beginning of Ephesians 5 Paul warns the saints in Ephesus who are faithful to Christ of turning back to a sinful way of life and thus receiving the wrath of God on the sons of disobedience. This indicates that those who are faithful in Christ are fully capable of turning back to a sinful way of life and as a result will have no inheritance in the kingdom of heaven.
“Therefore, laying aside falsehood, SPEAK TRUTH EACH ONE of you WITH HIS NEIGHBOR, for we are members of one another. BE ANGRY, AND yet DO NOT SIN; do not let the sun go down on your anger, and do not give the devil an opportunity. He who steals must steal no longer; but rather he must labor, performing with his own hands what is good, so that he will have something to share with one who has need. Let no unwholesome word proceed from your mouth, but only such a word as is good for edification according to the need of the moment, so that it will give grace to those who hear. Do not grieve the Holy Spirit of God, by whom you were sealed for the day of redemption. Let all bitterness and wrath and anger and clamor and slander be put away from you, along with all malice. Be kind to one another, tender-hearted, forgiving each other, just as God in Christ also has forgiven you.”
Ephesians 4:25-32 NASB
“Therefore be imitators of God, as beloved children; and walk in love, just as Christ also loved you and gave Himself up for us, an offering and a sacrifice to God as a fragrant aroma. But immorality or any impurity or greed must not even be named among you, as is proper among saints; and there must be no filthiness and silly talk, or coarse jesting, which are not fitting, but rather giving of thanks. For this you know with certainty, that no immoral or impure person or covetous man, who is an idolater, has an inheritance in the kingdom of Christ and God. Let no one deceive you with empty words, for because of these things the wrath of God comes upon the sons of disobedience.”
Ephesians 5:1-6 NASB