Summary: Jesus did not leave behind a powerless church when He ascended back to heaven. To the contrary, He imparted divine authority to those who follow Him, along with Holy Spirit power to accomplish great things for Him on this earth.
Matthew 28:18-20 Then Jesus came to them and said, “All authority in heaven and on earth has been given to me. Therefore [you] go and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, and teaching them to obey everything I have commanded you. And surely I am with you always, to the very end of the age.”
•• In the famous Great Commission, we see an impartation of authority from Jesus Christ to believers in Him. In some of His final words to His disciples before He ascended back to heaven, Jesus sends them forth into the world to preach, teach, baptize, and otherwise minister on His behalf — in essence, to teach the world "everything" (vs. 20) that Jesus had entrusted to His chosen disciples. The parallel Great Commission in Mark's Gospel (see next) confirms this transfer of heavenly authority to believers on earth.
Mark 16:15-20 [Jesus] said to them, “Go into all the world and preach the gospel to all creation. Whoever believes and is baptized will be saved, but whoever does not believe will be condemned. And these signs will accompany those who believe: In my name they will drive out demons; they will speak in new tongues; they will pick up snakes with their hands; and when they drink deadly poison, it will not hurt them at all; they will place their hands on sick people, and they will get well.” After the Lord Jesus had spoken to them, he was taken up into heaven and he sat at the right hand of God. Then the disciples went out and preached everywhere, and the Lord worked with them and confirmed his word by the signs that accompanied it.
•• Here again, the Great Commission sender is Jesus. Those who are sent forth to minister in all the world are His disciples — "those who believe" (vs. 17). And we are not sent powerless. No! If we believe Jesus and His promises, we will heal the sick, speak in new tongues, cast out demons, and much more as we bring the Gospel to the far corners of the earth. How? Because Jesus, who has "all authority in heaven and on earth" (Matt. 28:18) has given us this commission and the authority to fulfill it — even with the confirmation of supernatural signs.
•• Unfortunately, in too many churches today the saints are not taught that they, not just the pastor, are called and empowered to do the work of the ministry. The antidote for this is for believers to see in Scripture that Jesus has given all of us the power and authority to accomplish His work on earth, consistent with His unique callings and the spiritual enablements given to each one of us.
Luke 9:1-2; 10:19 When Jesus had called the Twelve together, he gave them power and authority to drive out all demons and to cure diseases, and he sent them out to proclaim the kingdom of God and to heal the sick... [and to 72 others He said, 10:19] I have given you authority to trample on snakes and scorpions and to overcome all the power of the enemy; nothing will harm you.
•• Not just to His apostles, but to a larger group of His followers (10:17) Jesus gave power and authority to proclaim the kingdom, to heal the sick, to cast out demons, and to overcome all the power of the enemy! And we have just seen (above) Jesus giving that same power and authority to believers to further the Great Commission in "all the world". That includes you and me!
John 14:12 Very truly I tell you, whoever believes in me will do the works I have been doing, and they will do even greater things than these, because I am going to the Father.
•• What works had Jesus been doing? Healing the sick, raising the dead, cleansing the lepers, casting out devils, proclaiming the kingdom of God, and more. Who else can do these works, and "even greater"? — the answer: "whoevever believes in [Jesus]". Not just His twelve apostles, not just pastors and church leaders, but whoever believes in Him! You can share the Gospel, confirmed with powerful signs, because Jesus has delegated this authority to believers. And the believer's authority is not restricted by our own natural limitations. Remember, it is God's authority given through Jesus to us.
Mark 13:34, KJV For the Son of Man is as a man taking a far journey, who left his house, and gave authority to his servants, and to every man his work, and commanded the porter to watch.
•• In the context above, Jesus was speaking to His disciples about the time between His first and second coming. He said He was going to "leave his house" — that is, return to heaven. And He gave to each of His servants on earth work to do and the authority to get it done. For this entire Church Age, Jesus has given spiritual authority to His servants on earth.
1 Corinthians 2:4-5 My message and my preaching were not with wise and persuasive words, but with a demonstration of the Spirit’s power, so that your faith might not rest on human wisdom, but on God’s power.
•• The apostle Paul refused to depend on his natural abilities (as prodigious as those were!). Let this be a lesson to us. Instead, he intended that people's faith would rest, not on his human wisdom, but on a Gospel preached with a confirming "demonstration of the Spirit's power". Let's see now the source of that Holy Ghost power that Jesus has promised to us.
Acts 1:5, 8 For John baptized with water, but in a few days you will be baptized with the Holy Spirit...  you will receive power when the Holy Spirit comes on you; and you will be my witnesses in Jerusalem, and in all Judea and Samaria, and to the ends of the earth.
•• Now let's look at some encouraging biblical examples of Christ's authority working effectively in the lives of believers.
1) Leading a soul to Jesus —John 4:28-30, 39 Then, leaving her water jar, the woman went back to the town and said to the people, “Come, see a man who told me everything I ever did. Could this be the Messiah?” They came out of the town and made their way toward him...  Many of the Samaritans from that town believed in him because of the woman’s testimony, “He told me everything I ever did.”
•• This Samaritan woman was herself a brand-new believer. But there was already within her as a believer the ability to say to her townspeople, "Come and see. Could this be the Messiah?" And they did come and hear Jesus speak, and many became believers in Christ, in great measure "because of the woman's testimony". This woman, not knowing theology, simply shared what faith she had, and souls were gathered to Jesus. If she could do this, so can we. Why? Because Jesus Christ has given us power from God and the authority to minister for Him with that delegated power here on earth.
2) Leading someone into the baptism with the Holy Spirit —Acts 9:10, 17 In Damascus there was a disciple named Ananias. The Lord called to him in a vision, “Ananias!” ...  Then Ananias went to the house and entered it. Placing his hands on Saul, he said, “Brother Saul, the Lord — Jesus, who appeared to you on the road as you were coming here — has sent me so that you may see again and be filled with the Holy Spirit.”
•• Ananias was simply "a disciple", a "devout man" (Acts 22:12, KJV), a believer in Jesus. Yet the Lord used him to heal Saul's blindness and to minister the baptism with the Holy Spirit to Saul (who later became the apostle Paul).
3) Casting out demons —Mark 16:17 And these signs shall follow them that believe; In my name shall they cast out devils.
•• Believers, not just apostles, can cast out demons. My wife and I and another believer once cast four demons out of a young woman who was terribly demon-possessed. Within minutes of her deliverance, she was saved and baptized with the Spirit, speaking in tongues, and crying joyfully, "This is what I've always wanted!" How could we, mere human beings, force demons from the spirit world to leave that woman? The answer is simple: by our own power we couldn't! But Jesus said to His disciples, "I have given you authority to trample on snakes and scorpions and to overcome all the power of the enemy" (Luke 10:19). Jesus confirmed this promise in the Great Commission: "These signs will accompany those who believe: In my name they will drive out demons" (Mark 16:17).
4) Healing the sick —Mark 16:17-18, KJV And these signs shall follow them that believe; In my name ...  they shall lay hands on the sick, and they shall recover.
•• It is the privilege of all believers ("them that believe") to lay hands on the sick and see them healed. In the churches that I pastored, I always invited the congregation to participate in the post-service ministry, including praying for the sick. Among them might very well be some with the Holy Spirit-given "gifts of healing" (1 Corinthians 12:9).
5) Have prayers answered —James 5:13a, 16b Is anyone among you in trouble? Let them pray... [16b] The prayer of a righteous man is powerful and effective.
•• Remember, believers have authority given by Jesus, the possessor of all authority in heaven and on earth. This applies to our prayer lives as well, where we find that the prayer of "a righteous man" is powerful and effective. Be confident as you pray, come boldly to His throne of grace in your times of need (Hebrews 4:16).
6) Manifesting gifts of the Holy Spirit —Acts 21:8-9 ...we reached Caesarea and stayed at the house of Philip the evangelist, one of the Seven. He had four unmarried daughters who prophesied. [Amplified: "who had the gift of prophecy"]
•• Four young ladies, each of whom had the gift of prophecy. This is consistent with Peter's great Pentecost sermon where, quoting the prophet Joel, he says, "...I will pour out my Spirit on all people. Your sons and daughters will prophesy..." (Acts 2:17).
•• As a pastor in Pentecostal churches I have seen literally hundreds of Spirit-filled believers, young and old, men and women, being used in the gifts of the Holy Spirit. Not just pastors and elders, but the members of the church broadly — born-again Christians, aware of the authority Jesus has given believers, and finding the source of spiritual power in the baptism with the Holy Spirit.
Matthew 7:19-20 Then the disciples came to Jesus in private and asked, “Why couldn’t we drive it out?” He replied, “Because you have so little faith. Truly I tell you, if you have faith as small as a mustard seed, you can say to this mountain, ‘Move from here to there,’ and it will move. Nothing will be impossible for you.”
•• Many Christians, like those disciples, may be thinking, "Why couldn't we...?" And Jesus replies quite simply that's it's a matter of faith.
• Do you believe that Jesus has given authority to His servants? (Mark 13:34)
• Do you believe that He gives us a large measure of divine power in the baptism with the Holy Spirit? (Acts 1:5, 8)
• Do you believe that, as you go forth with the Good News, He will confirm the word with supernatural signs? (Mark 16:20)
• Do you believe that those with faith in Jesus will do His works and "even greater"? (John 14:12)
•• Jesus told his doubting disciples that, if they had faith, they could "move mountains", and nothing would be impossible for them.
•• How can this be? Simply because our resurrected Savior, who possesses all authority in heaven and on earth (Matt. 28:18-20) has chosen to impart authority to His servants, so that we might go forth in power to expand the kingdom of God on this earth. And you are one of those servants that our Lord has called and empowered to be effective ambassadors for Christ to this lost world.