God does not break His promise,but some people break their covenant with God,by not doing what is required of them in the eyes of God.
The Bible says we will be saved if we continue in the goodness of God,and we do that by allowing the Spirit to lead us.
Some people deny the Spirit leading them,which the Bible says they have a form of godliness,but deny the power thereof,ever learning and never able to come to the knowledge of the truth,and lovers of pleasures more than lovers of God,which Jesus denied some people that claimed Him,because He said they were workers of iniquity,and did not do the will of the Father,and 5 of the 10 virgins were only granted access to heaven,which were the ones that oil in their lamp,which is the word of God taught by the Spirit,and oil in their vessels,which they allowed the Spirit to lead them.
But all we have to do is allow the Spirit to lead us,and we have no problem,but some people break their covenant with God.
God will not break His promise if we do what is right,because the gifts and calling of God are without repentance,which means once God calls you,and you are saved,He will not turn from it.
Once saved always saved cannot be true,for then God's kingdom would not be true love,and the Bible says God is not willing that any perish,but all come to be repentance,and be saved,and Jesus is the savior of all people,and lights every person that comes in this world,which means that everybody can be saved,and the Bible says whosoever will can be saved,and anybody that calls on the Lord can be saved.