I am at a complete loss to understand or justify the translation of "failing to grasp" in Gal 5:4. The Greek is quite simple:
κατηργήθητε ἀπὸ Χριστοῦ οἵτινες ἐν νόμῳ δικαιοῦσθε, τῆς χάριτος
The operative word here is the final one whose lexical form is ἐκπίπτω which literally means, "to leap out/off". It occurs just 10 times in the NT:
- Acts 12:7 - Suddenly an angel of the Lord appeared and a light shone in the cell. He tapped Peter on the side and woke him up, saying, “Get up quickly.” And the chains fell off his wrists.
- Acts 27:17 - which having taken up, they began using supports, undergirding the ship. And fearing lest they should fall into the sandbars of Syrtis, having lowered the gear, thus they were driven along.
- Acts 27:26 - But it behooves us to fall upon a certain island."
- Acts 27:29 - And fearing lest we might fall somewhere on rocky places, having cast four anchors out of the stern, they were praying for day to come.
- Acts 27:32 - Then the soldiers cut away the ropes of the lifeboat, and allowed her to fall away.
- Rom 9:6 - And it is not as that the word of God has failed/fallen. For not all who are of Israel, are these Israel.
- Gal 5:4 - Whoever are being justified in the Law, you are severed from Christ; you have fallen away from grace.
- James 1:11 - For the sun rises with scorching heat and withers the plant; its flower falls and its beauty is lost. So too, the rich man will fade away in the midst of his pursuits.
- 1 Peter 1:24 - because, "All flesh is like grass, and all the glory of it like the flower of grass. The grass withers, and the flower falls away,
- 2 Peter 3:17 - Therefore beloved, knowing this beforehand, you beware, lest you should fall from the own steadfastness, having been led away by the error of the lawless.
Since God loves all men and has extended grace to all men and wants all to repent (John 12:32, Acts 17:30, Rom 11:32, 2 Cor 5:14, 1 Tim 2:3, 4, 6, Titus 2:11, Heb 2:9, 2 Peter 3:9, etc), a "fall from grace" is not a failing of God but the failing of man to respond to the prompting and drawing of God.