The disciples were using natural reasoning and recognized that they didn't have the ability to minister to the multitude's need for food. Jesus did have the ability and the willingness to minister to their needs, so the multitude did not need to depart.  All of their needs could be met through Jesus.

The same is true today.  Some disciples today are sending the multitudes to the world to meet their physical needs (finances, health, counseling, etc.) and proclaiming that God only meets spiritual needs.  But, "they need not depart."  The Lord is willing and able to heal our bodies, prosper us financially, or counsel us from His Word in any area of our life where we have needs.

Before we can be a blessing, we have to be blessed (Genesis 12:2). One of the purposes of God's prosperity in our lives is so that we can be a blessing to others.  The Bible teaches us to walk in God's love towards all men, believers and non-believers both.  Jesus told us to love our enemies (Matthew 5:44).  In Galatians 6:10 Paul places a priority on helping fellow Christians. This does not lessen our responsibility to show God's love to non-believers.  Paul is simply saying "charity must start at home."  It would be hypocritical to step over hurting brothers and sisters in the Lord to find unbelievers to minister to.

God didn't just give us something that He had; He gave Himself. And what was God's motive for giving?  It wasn't because of His need, but ours.  He was motivated out of love for us (John 3:16).  In the same way, we should be encouraged to give unselfishly of ourselves. Pray for Divine appointments, to be used of God to touch someone's.