“And whoever will receive one such little child in my name receives me.”
(Some of the verbs continue as second aorists and could therefore be translated as perfects - ‘whoever has received one such little child in My name receives Me' - thinking, however, in this case of an action that will be ‘past' in the future, for a major purpose of the second aorist is in order to be ‘timeless' and rather to indicate a particular action, a purpose retained in the translation).
‘One such little child.' This probably refers back to those who have ‘become as little children' (Matthew 18:4), that is, all true disciples. Once they have chosen to become His children He has a special care for them. Thus from now on He describes them as ‘little ones'.
‘In My Name.' Compare here the one who gives a cup of cold water to a child ‘in the name of a disciple', that is because the child is His disciple (Matthew 10:42). Here then His disciples are to receive their fellow-disciples ‘because they are His and bear His name'. They are ‘received in His Name' because they bear the name of Jesus, that is they declare themselves to be His followers, to be ‘Christ's men'. They believe in Him and declare Him to be their Master.
The word ‘receive' regularly means ‘to receive with hospitality, to welcome' (compare and contrast Matthew 10:14), but its meaning here is wider. Those who ‘receive' others offer an open-hearted acceptance. And when they do that to one who believes in Him, however humble, they receive Jesus Himself (‘Me' is emphatic). We can compare also how when they are persecuted, Jesus Himself is seen as being persecuted (Acts 9:4-5). And when they are in need and fed and clothed etc. it is as though it was done to Him (Matthew 25:35-36). The oneness of His people with Himself is made very clear here. In Jesus' eyes what is done to His true people is done to Him.