He comes "in the evening" so that they would have time to gather all together. He comes "when the doors were shut" in order to show that He also rose in the same way, when the stone lay upon the tomb.
One might wonder how they did not take Him for a ghost? But first of all, the woman who had preceded them produced in them a strong faith. Then, He appeared to them in a gentle form and by His very voice calmed their troubled thoughts, saying "Peace to you," that is, do not be troubled. By this He reminds them of the word which He said to them before His suffering: "My peace I give to you" (John 14:27).
It is worth knowing why He appears to the disciples not in Galilee, but in Jerusalem. For Matthew (Matt. 26:32) and Mark (Mark 14:28) say that He promised to see them in Galilee. How then does He appear in Jerusalem? Some answer: "So what? He did not say that I will see you only in Galilee and not in Jerusalem. Therefore, this is an abundance of love, not an occasion for accusation of falsehood." Then one can say that He promises to appear in Galilee to all the disciples, but in Jerusalem He appeared only to those belonging to the Twelve. Thus, there is no disagreement here. For in Galilee He appeared to all, and in Jerusalem to the Twelve. And since the appearances were many, some evangelists described some appearances, and others described others. Sometimes two evangelists also report the same thing, but what one has said in abbreviated form, the other supplements.
Jn. 20:20. Having said this, He showed them His hands and feet and His side. The disciples rejoiced, having seen the Lord.
The disciples were glad when they saw the Lord. And about this He also foretold them before the Passion: "I will see you again, and your heart shall rejoice" (Jn. 16:22).
Jn. 20:21. Jesus then said to them a second time: Peace be with you!
And since they had an irreconcilable war with the Jews, He again says to them: "Peace." Just as He said to the women: "Rejoice" (Matt. 28:9), because their sex was in sorrow, so to the disciples He gives "peace" because of the war which they had with them and which all will have. Thus, it is fitting for women to rejoice, because they are condemned to give birth in sorrow, and for men to be at peace because of the war for the cause of preaching.
Jn. 20:21. As the Father has sent Me, so I also send you.
He shows at the same time the good consequences of the Cross as well; this is peace. And since peace was acquired through the Cross, I am sending you to preach. And for their consolation and encouragement He says: "As the Father has sent Me, so I also send you." You are taking upon yourselves My work; therefore be vigilant, for I will be with you. Note the sovereign authority. He did not say "I will beseech My Father, and He will send you," but rather "I am sending you."
Jn. 20:22. Having said this, He breathed on them, and says to them: Receive the Holy Spirit.
He breathes and gives them the Holy Spirit. Now He imparts to them not the perfect gift of the Holy Spirit, for He will give them that at Pentecost, but makes them capable of receiving the Spirit. For the words "receive the Holy Spirit" mean the same as: be ready to receive the Spirit.
Jn. 20:23. Whosesoever sins ye remit, they are remitted unto them; and whosesoever sins ye retain, they are retained.
One could also say that He gave them a certain authority and spiritual grace, only not to raise the dead and perform miracles, but to forgive sins. Therefore He also added: "Whose sins you forgive, they are forgiven," showing that He gave them this particular kind of spiritual gift—the forgiveness of sins. But after His ascension, the Spirit Himself descended and abundantly granted them the power to work miracles and every other gift.
Note, if you will, the dignity of priests — it is Divine. For to forgive sins is the work of God. Thus, they must be honored as God. Even if they were unworthy, what of it? They are ministers of Divine gifts, and grace acts through them, just as it once spoke through Balaam's donkey (Num. 22:28–30). Therefore, our unworthiness does not hinder grace. And since grace is bestowed through priests, they must be honored.
Jn. 20:24. Thomas, one of the twelve, called the Twin, was not there with them when Jesus came.
Thomas was not with the disciples. Probably he had not yet returned to them from the dispersion that had taken place.
What does the remark "called the Twin" mean? It is the meaning of the name Thomas. For just as Cephas means rock, so Thomas means twin. The Evangelist mentions this meaning of Thomas's name, incidentally, to show us that he was somewhat incredulous and had such a character from his very birth, as the name itself indicates.
Jn. 20:25. The other disciples said to him: we have seen the Lord. But he said to them: unless I see in His hands the wounds from the nails, and put my finger into the wounds from the nails, and put my hand into His side, I will not believe.
When the other disciples spoke about the Lord, Thomas did not believe not because he considered them liars, but because he considered the matter of the resurrection impossible. This is also why he is accused of immoderate curiosity. For just as believing too quickly is reckless, so stubbornly persisting is savage and crude.
See, he did not say "I do not believe my eyes," but added — "unless I put my hand." But how did he know that there was a wound in the side? He heard this from the disciples.
Jn. 20:26. After eight days His disciples were again in the house, and Thomas with them. Jesus came, when the doors were shut, stood in their midst and said: Peace be unto you!
For what reason does the Lord appear to him not immediately, but after eight days? So that he, heeding the instruction of his fellow disciples and hearing the same thing, would be inflamed with greater desire and become firmer in faith for the future.
Jn. 20:27. Then He says to Thomas: bring your finger here and look at My hands; bring your hand and put it into My side; and do not be unbelieving, but believing.
The Lord, wishing to show that He was with them even when Thomas was speaking words of his unbelief before his fellow disciples, does not wait until He hears something similar from him, but Himself fulfills in advance what Thomas desired, and uses his own words. And observe, first He speaks with reproach: "Reach here your hand," but then He instructs: "Be not faithless, but believing."
From this it is clear that the doubt arose from unbelief, and therefore it is in vain that some speak in defense of Thomas, saying that he was slow to believe due to his thoroughness. For behold, the Lord calls him unfaithful.