One thing we cannot do is to save people. Let us stop acting like the Savior. Something is wrong when we have taught our disciples that when they encounter problems the first person they run to is you and not Jesus. Only Jesus can save us from our sin. Only Jesus has conquered sin and death.
Another thing we cannot do is solve. Sin is too big a problem to be solved. Only Jesus knows the human heart and it is only through the Holy Spirit is it revealed to us.
One thing we can do is serve. We can by the grace of God, be the loving brother and sister and the one to graciously point people to Jesus.