On the day he was circumcised he received the name of JESUS, the same which had been appointed him by the angel Gabriel before he was conceived.
And she shall bring forth a son: and thou shalt call his name JESUS. For he shall save his people from their sins. Now all this was done that it might be fulfilled which the Lord spoke by the prophet, saying: Behold a virgin shall be with child, and bring forth a son, and they shall call his name Emmanuel, which being interpreted is, God with us. Matthew 1:21-23 DRV
The reason of his being called Jesus is mentioned in the gospel: For he shall save his people from their sins. This he effected by the greatest sufferings and humiliations; having humbled himself, as St. Paul says, “not only unto death, but even to the death of the cross, for which cause God hath exalted him, and hath given him a name which is above all names; that at the name of Jesus every knee should bow: agreeably to what Christ says of himself, “All power is given unto me in heaven and in earth.”
(Adapted from Butler’s Lives of the Saints)