The -unfathomable riches of Christ- refers to a track that is visible enough to be noticed at times, and yet ultimately- in this life- untrackable-unable to be fully known-.

This does not mean that in His selection of us that God pushes others away. Rather, it means that through His electing grace, the Lord brings dead sinners to life- He resurrects them- unto a specific end-purpose which cannot be thwarted -cf. Jn. 15-16a- 1 Pet. 1-4-5- 2-6- 3-18-

That which God's people were to -stand firm in-- that which here is identified as the -grace of God-- is nothing less than the teaching of this -brief epistle- and so, more generally, the teaching of the Word of God-

What Satan might mean for evil, God uses for good in our lives unto the ultimate end of fitting us for glory- Accordingly, the call of Scripture is to work with the trials and difficulties of this life- really to work actively, along with God- that the trial might produce in us growth, maturation, trust, and reliance upon Christ -cf. James 1-2-4- Romans 5-3-4--

An important part of God's grace is divine enablement by which the saved sinner is able to grow in their walk, serve the Lord, bring about His kingdom work, and so glorify God- And it is this facet of grace that is being used in the text before us.

The core kingdom principle is this- Grace is given to those who cannot help themselves-

1 Peter 5-1-5-We tend to view the fall of man exclusively as damaging man's relationship towards God, we must also see that the fall had a profound impact upon man's relationships with others.