2. Be--Greek. "Become," what thou art not, "watchful," or "wakeful," literally, "waking."
      the things which remain--Strengthen those thy remaining few graces, which, in thy spiritual deadly slumber, are not yet quite extinct [ALFORD]. "The things that remain" can hardly mean "the PERSONS that are not yet dead, but are ready to die"; for Re 3:4 implies that the "few" faithful ones at Sardis were not "ready to die," but were full of life.
      are--The two oldest manuscripts read, "were ready," literally, "were about to die," namely, at the time when you "strengthen" them. This implies that "thou art dead," Re 3:1, is to be taken with limitation; for those must have some life who are told to strengthen the things that remain.
      perfect--literally, "filled up in full complement"; Translate, "complete." Weighed in the balance of Him who requires living faith as the motive of works, and found wanting.
      before God--Greek, "in the sight of God." The three oldest manuscripts, Vulgate, Syriac, and Coptic, read, "before (in the sight of) MY God"; Christ's judgment is God the Father's judgment. In the sight of men, Sardis had "a name of living": "so many and so great are the obligations of pastors, that he who would in reality fulfil even a third of them, would be esteemed holy by men, whereas, if content with that alone, he would be sure not to escape hell" [JUAN D'AVILA]. Note: in Sardis and Laodicea alone of the seven we read of no conflict with foes within or without the Church. Not that either had renounced the appearance of opposition to the world; but neither had the faithfulness to witness for God by word and example, so as to "torment them that dwelt on the earth" (Re 11:10).

JFB.