Jesus was really emphasizing this message by repeating twice that this is the truth. If we are able to do even greater things than Jesus did while he walked the earth then what is stopping us, and what exactly are those "greater things?" A large part of what Jesus did was healing and letting people know that the kingdom of God was at hand or in the midst of us, not some external, distant future event. "Behold, now is the acceptable time" (2 Cor 6:2).
We have the ability and divine right, right now, in the present moment, to ask God to remove the obstacles to being one with God, ending the separation that we consciously or unconsciously created, and be made brand new. Our own mind is the only thing that can stop us. We may not realize that we are inwardly controlled by old conditioning, limiting beliefs and thoughts, but if we turn to the Spirit and ask to be cleared of limitations, restrictions, and obstructions, the Spirit can bring to our awareness any places we are separating ourselves from the light of God.
"If you remain true to God, God will lead you straight through every barrier into the inner chamber of the knowledge of Himself; but there is always this point of giving up convictions and traditional beliefs" (Oswald Chambers)
Instead of looking at life, ourselves and others from a human point of view, through the conditioning of the world, parents, religion, authorities, and education, we can elevate our perspective to see from the higher view. "From now on, therefore, we regard no one from a human point of view; even though we once regarded Christ from a human point of view...therefore, if any one is in Christ, she is a new creation; the old has passed away, behold, the NEW has come" (2Cor 5:16-17).
We are limiting God by our limiting thoughts and beliefs about God and what is possible. Expand your possibilities. Ask to see through the eyes of Christ. Start looking at yourself and others from the divine perspective. Jesus said "Come and See!" What greater things can you imagine? What is stopping you?