To 'be strengthened,' as in Genesis 21:18, signifies being supported.

In Isaiah 41:10, this signifies to give power and intelligence from the omnipotence and omniscience of the Divine Good and Truth. (Apocalypse Explained 298[10])

(Referências: Arcana Coelestia 2698)

2698. 'And strengthen your hand in him' means support received from this. This is clear from the meaning of 'being strengthened' as being given support, and from the meaning of 'hand' as power, dealt with in 878, which is the source of support. 'In him', that is, in the boy, means from it, that is to say, from the spiritual as regards truth. Those who experience internal grief and experience despair because truth is taken away from them are uplifted and supported solely by truth, for it is for that same truth that they suffer grief and despair. In the case of those governed by an affection for good, the good with them desires good, as a person hungers for bread; but in the case of those governed by an affection for truth the good with them desires truth as a person thirsts for water. What 'strengthening your hand in him' means here will not be understood by anyone except from the internal sense.