He knows the end from the beginning so He can’t change His mind or take back something He’s given. Everything He says has to agree with everything else He says.
For example, if the Bible says it’s God who makes us stand firm in Christ, that He anointed us, set His seal of ownership on us and put His Spirit in our hearts as a guarantee of what’s to come (2 Cor. 1:21-22), then it can’t say that we can walk away from our salvation or have it taken away from us someplace else.
Agreed. God has placed His seal on us, and put His Spirit in our hearts as a pledge of what is to come. Because God has set His seal upon us by the indwelling Holy Spirit, we have a new birth into His family.
It's only human to have times of weak faith or doubts, but God is faithful, He will not deny Himself. He perfects and matures our faith. The genuine believer may go through times of doubt but he/she will not remain there. The indwelling Holy Spirit will compel us to return to the Lord who loves us and who is always drawing us to Himself. He will not leave us or forsake us.