Martin Luther on Psalms 121:5

Verse. 5. The Lord is thy keper and he is thy shadowe (or protection) at thy right hand.

In this verse he setteth foorth more at large, the certainty of Gods ready helpe and protection. Wherin, speaking to euery one priuatly, he sayth: The Lord is thy keeper: that no man should doubt to apply that vnto him selfe for his owne comforte, which pertaineth to al Israel. He is called the shadow at thy right hand, to teach thee that he is at hand and standeth euen by thy side ready to defend thee. Or else: the Lord is thy shadow at thy right hand: That is, he prospereth all thy affaires, he giueth successe to all thou takest in hand. If thou be a preacher & a teacher in ye Church of God: if thou trauell in thy vocation vprightly and with a good conscience to prouide for thy selfe and thy family, thou shalt not lack thy crosses. But be of good comfort: for the Lord hath promised to be on thy right hand: he will ayde thee and succour thee in all things that thou shalt either doe or suffer.

But here againe we must remember (as I said before) that these things are spoken and taught in vaine, except we first thinke our selues to be, as it were vtterly forsaken and destitute of al help and succour. Therefore, when he speaketh of this tender care that the Lord hath ouer his in keping, in shadowing, in defēding them that they perish not, he meaneth therewithall that they are such as seeme to them selues so to be forsaken and neglected of God, as if he had no care of them at all. This is therefore a sweete doctrine and full of consolation, that the Lord sheweth him selfe to knowe and to pittie our miseries and calamities, and commaundeth vs to beleeue that he is our shadowe to couer & defend vs against all perils & daungers. In him therefore let vs assuredly trust, with comfortable expectation of most ioyfull deliuerance: who hath promised to be with vs, with a fatherly care to prouide for vs, to defend vs, to strengthen, to succour and to comfort vs in all our troubles, afflictions and calamities.