4 For it is impossible, in the case of those who have once been enlightened and have tasted of the heavenly gift and have been made partakers of the Holy Spirit, 5 and have tasted the good word of God and the powers of the age to come, 6 and then have fallen away, to restore them again to repentance, since they again crucify to themselves the Son of God and put Him to open shame. Hebrews 6.
It is good to know those whom God calls internally and has freely given faith and holiness to, He likewise keeps with such great care, that it is impossible for any true believer to totally and finally fall away from that faith and holiness once it has begun, and thereby forfeit the salvation appointed for him.
But the Lord is faithful, and He will strengthen and protect you from the evil one. 2 Thess 3:3.
By grace, God keeps those He redeemed, regenerated, and sanctified. Though we are weak and prone to fall away, by "internally" the most powerful efficacy of His Spirit.
Therefore, you shall keep the commandments of the Lord your God, to walk in His ways and to fear Him. Deut 8:6.
Unlike those in Heb 6 who are called externally.