He rebuked them for their unbelief

Acts of the Apostles 4:13-21. 

Observing the boldness of Peter and John and perceiving them to be uneducated, ordinary men, the leaders, elders, and scribes were amazed, and they recognized them as the companions of Jesus.
Then when they saw the man who had been cured standing there with them, they could say nothing in reply.
So they ordered them to leave the Sanhedrin, and conferred with one another, saying,
"What are we to do with these men? Everyone living in Jerusalem knows that a remarkable sign was done through them, and we cannot deny it.
But so that it may not be spread any further among the people, let us give them a stern warning never again to speak to anyone in this name."
So they called them back and ordered them not to speak or teach at all in the name of Jesus.
Peter and John, however, said to them in reply, "Whether it is right in the sight of God for us to obey you rather than God, you be the judges.
It is impossible for us not to speak about what we have seen and heard."
After threatening them further, they released them, finding no way to punish them, on account of the people who were all praising God for what had happened.

Psalms 118(117):1.14-15.16ab-18.19-21. 

Give thanks to the LORD, for he is good,
for his mercy endures forever.
My strength and my courage is the LORD,
and he has been my savior.
The joyful shout of victory
in the tents of the just:

"The right hand of the LORD is exalted;
the right hand of the LORD has struck with power."
I shall not die, but live,
and declare the works of the LORD.
Though the LORD has indeed chastised me,
yet he has not delivered me to death.

Open to me the gates of justice;
I will enter them and give thanks to the LORD.
This is the gate of the LORD;
the just shall enter it.
I will give thanks to you, for you have answered me
and have been my savior.

Holy Gospel of Jesus Christ according to Saint Mark 16:9-15. 

When Jesus had risen, early on the first day of the week, he appeared first to Mary Magdalene, out of whom he had driven seven demons.
She went and told his companions who were mourning and weeping.
When they heard that he was alive and had been seen by her, they did not believe.
After this he appeared in another form to two of them walking along on their way to the country.
They returned and told the others; but they did not believe them either.
(But) later, as the eleven were at table, he appeared to them and rebuked them for their unbelief and hardness of heart because they had not believed those who saw him after he had been raised.
He said to them, "Go into the whole world and proclaim the gospel to every creature."

"He rebuked them for their unbelief "

Where signs and testimonies abound, there is less merit in believing. God never works marvels except when they are a necessity for belief. Lest his disciples go without merit by having sensible proof of his resurrection, he did many things to further their belief before they saw him.
     
Mary Magdalene was first shown the empty sepulcher, and afterward the angels told her about the resurrection so she would, by hearing, believe before seeing. As St. Paul says: “Faith comes through hearing” (Rom10,17) . And though she beheld him, he seemed only an ordinary man, so by the warmth of his presence he could finish instructing her in the belief she was lacking

      And the women were sent to tell the disciples first... And journeying incognito to Emmaus with two of his followers, he inflamed their hearts in faith before allowing them to see him. Finally he reproved all his disciples for refusing to believe those who had told them of his resurrection. And announcing to Thomas that they are blessed who believe without seeing (Jn 20,29), he reprimanded him for desiring to experience the sight and touch of his wounds.