Making sense of all the data on salvation and assurance is a challenge. Most systems do not factor in all the data.
Some folk focus on the warnings and point out that the New Testament teaches we must persevere to be saved [and therefore, we may lose our salvation].
Others focus on the many promises that God will keep us safe [and therefore we cannot lose our salvation].
But a few folk put these warnings and promises together and come up with this:
1. Salvation is assured to those who trust in Christ alone. Consider Romans 8:28-39 among many passages in the New Testament.
2. But we are warned that only those who persevere to the end will be saved. Hebrews chapters 6 and 10 for example.
3. However God in his mercy ensures that we will persevere through giving us these threats and promises to keep us on the path. But this perseverance itself is God's doing. I think Philippians 2:12-13 and many other passages teach this.
Many Calvinist and Puritan authors have taught the above.