John 20:19

Then the same day at evening
The same day Christ rose from the dead, and appeared to Mary; at the evening of that day, after he had been with the two disciples to Emmaus, about eight miles from Jerusalem, and they had returned again to the rest; and after there had been such a bustle all day in Jerusalem, about the body of Jesus; the soldiers that watched the sepulchre, giving out, by the direction of the elders, that the disciples of Christ had stolen away the body, while they slept:

being the first day of the week;
as is said in ( John 20:1 ) and here repeated, to prevent any mistake; and that it might be clear what day it was the disciples were assembled together, and Christ appeared to them:

when the doors were shut;
the doors of the house where they were, which it is plain was in Jerusalem, ( Luke 24:33 ) but whether it was the house where Christ and his disciples ate the passover together, or whether it was John's home or house, to which he took the mother of Christ, since he and Peter, and the rest, seem to be afterwards together in one place, is not certain: however, the doors were shut; which is not merely expressive of the time of night, when this was usually done; but signifies that they were really locked and bolted, and barred, for which a reason is given as follows:

where the disciples were assembled for fear of the Jews;
after their scattering abroad upon the taking of Christ, and after his crucifixion was over; and especially after the report of his body being took away, they gathered together, and made fast the doors of the place, lest the Jews should come in upon them, and surprise them; for they might fear, that since they had took away their master's life, theirs must go next; and especially since it was rumoured abroad that they had stole away his body, they might be under the greater fear, that search would be made after them, and they be apprehended and brought into trouble on that account:

came Jesus and stood in the midst of them;
on a sudden, at once, and when they had no thought or fear of anyone's coming upon them, without some previous notice; but he being the Almighty God, did, by his omnipotent power, cause the bars and bolts, and doors, in the most secret and unobserved manner, to give way to him, and let him in at once among them: when as a presage and pledge of the accomplishment of his promise to be with, and in the midst of his, when met together, either in private or public, he stood and presented himself in the midst of them: and to let them know at once he was no enemy,

he saith unto them, peace be unto you:
(Mkl Mwlv) , "peace be unto you", is an usual form of salutation among the Jews; see ( Genesis 43:23 ) expressive of all prosperity in soul and body, inward and outward, spiritual and temporal; and here may have a special regard to that peace he said he gave unto them, and left with them, upon his departure from them; and which he had obtained by the blood of his cross, and now preached unto them.