|Quóniam ángelis suis mandábit de te.||For He shall command His angels concerning you.|
mandabit = He shall command, future tense.
angelis suis = to His angels. Somewhere along the wall bordering the Vatican City State there is this inscription: “Angelis suis mandabit de te, ut custodiant te in omnibus viis tuis.” / “He shall command His angels concerning you, to guard you in all your ways.” The verb mando,are takes the dative case, which is why it does not say angelos suos as one might expect.
de te = concerning you. The preposition de can mean regarding, concerning, about, etc.