Like the word "all", the word "salvation" has different senses.
In the eternal, unchanging sense, God determined whom He would save before creation began. Being omniscient, omnipotent, & omnipresent eliminates the possibility of chance & randomness
from His vantage point. From our perspective, chance is the only way to explain things we don't completely understand in the way God can & does.
That being said, the scriptural evidence is found in more than one place, but Ephesians reveals what I've just said here:
Eph 1:4: According as he hath chosen us in him
before the foundation of the world, that we should be holy and without blame before him in love:
5: Having
predestinated us unto the adoption of children by Jesus Christ to himself,
according to the good pleasure of his will,
6: To the praise of the glory of his grace, wherein he hath made us accepted in the beloved.
Our salvation is according to His will, not ours. God does not react dependant upon a creature of His own making.
Nothing resists His totaly sovereign will.
The immediate objection is usually that that would render us robots without a will of our own. Nothing could be further from the truth. Predestination does not eliminate personal will, it simply directs it.
Further in this objection is the query:", Why doth he yet find fault? For who hath resisted his will? "(Romans 9)
How can He judge us guilty of what He has determined for us to do?
The answer is extremely offensive to those who believe they are the captains of their own destiny as it pertains to the jurisdictional fact of God's total sovereignity:"
20: Nay but, O man, who art thou that repliest against God? Shall the thing formed say to him that formed it, Why hast thou made me thus?
21: Hath not the potter power over the clay, of the same lump to make one vessel unto honour, and another unto dishonour? "
Leaving us with only the ability to ask "Why would He do that?"
Answer:
22: What if God, willing to shew his wrath, and to make his power known, endured with much longsuffering the vessels of wrath fitted to destruction:
23: And that he might make known the riches of his glory on the vessels of mercy, which he had afore prepared unto glory,
24: Even us, whom he hath called, not of the Jews only, but also of the Gentiles?
A verse that illustrates that God's sovereignity doesn't cancel out personal responsibility is this one:
Ac 2:23 - Him, being delivered by the
determinate counsel and foreknowledge of God, ye have taken, and
by wicked hands have crucified and slain:
We can conclude that motivation is the key.
God is responsible for the murder of His Son, but He is not guilty of it because it was an evil He created with good intent. His good intentions are toward those He loves, not toward those He hates.
Isaiah 45:
7: I form the light, and create darkness: I make peace, and create evil: I the LORD do all these things.
When God creates evil, He does it out of good intention. When men act wickedly, they do it out of evil intent.
The idea that we are so valuable to him that He would give us self-sovereignity (free will) is narcisstic in the extreme.
All the scriptural exhortations & admonitions about our behavior are not disproving predestination & proving free will. Predestination is not an excuse for bad behavior or apathy.
We experience the grace of election when we are regenerated by saving grace, which is when we are first thoroughly convicted of both His love & our desperate need for it, followed by our desire to know & obey Him, not out of fear so much as out of gratitude. To say that our salvation depends in any way upon ourselves is to say Christ's death only made our salvation a possibilty & that it is ourselves who make it a reality, earning it by our obedience. That eliminates salvation as an act of mercy & makes it an act of merit.
The verses that sound like you can lose your salvation are usualy talking about losing rewards in heaven, not losing your ticket in, a ticket that Christ purchased Himself on the cross.