In the Gospel according to John we can see what Jesus said to His disciples, those whom He had called to follow Him, because in this way they would learn what Jesus wanted to teach them.
In the disciples there was always an enormous concern, this happened because Jesus spoke to them of many things that would happen, in the not too distant future. For these reasons they were very concerned. That is why the words that Jesus says in the following verse:
Let not your heart be troubled: ye believe in God, believe also in me.
John 14:1 (KJV)