Paul had a 'heavenly vision'. But there are those who '... speak a vision of their own heart, not from the mouth of the Lord' (Jeremiah 23:16 NKJV). So you must be sure you are operating according to God's plan, not your own nor somebody else's. The story of the Tower of Babel teaches us two things. First, that when people make up their mind to do something, they often succeed; and second, that succeeding doesn't mean that you're in the will of God. The word Babel (confusion) means others can think you're right, yet you're wrong. You ask, 'But isn't it all right to make plans and set goals?' Yes, but your plans and goals should come out of a vision that God has given you.
When Paul said, 'I was not disobedient unto the heavenly vision', he meant that there's only one acceptable response to God's plan - obedience! Partial obedience, selective obedience or delayed obedience are still all disobedience. William Carey, who is considered the father of modern missions, gave up comfort and fortune to go to India and introduce the gospel. One of his more memorable quotes is: 'Expect great things from God; attempt great things for God' But you can only say that with confidence when you know what God has called you to do. What He ordains, He sustains! When you set your own goals you lack a heartfelt confidence that God is doing the work, so you wear yourself out thinking it's all up to you. However, when you know God has given you a vision for your life, you trust Him, even when you can't see any way to bring it to pass.
When God gives you a vision, 1) it will interrupt you. Sometimes God will speak in a voice you can't tune out. Other times, like Jonah, God will let you go to the bottom to get your attention. Either way, things won't go right until you say yes to Him 2) it will illuminate you. You may not like what God says. Ananias didn't like going to pray for Saul of Tarsus, a man with the power to put Christians to death. But God said, 'Go, for he is a chosen vessel... I will show him how many things he must suffer for My name's sake' (Acts 9:15-16 NKJV). Notice the word 'suffer'. The Devil isn't going to send you a congratulatory telegram because you have decided to do God's will, so be prepared for attack 3) it will inspire you. You will accomplish things you never dreamed possible. Look at Gideon. When God found him he was hiding in a winepress (Judges 6:11 NKJV); not exactly a promising start. When the angel called him 'a mighty man of valour' (v 12 NKJV), he replied, 'I am the least in my father's house' (v 15 NKJV). When the angel said, 'The Lord is with you,' he replied, 'If the Lord is with us, why then has all this happened to us?' (vv 12-13 NKJV). When he finally took the job, he wondered, 'How can so few of us defeat so many of them?' Yet at that very moment his enemies were having nightmares about him (Judges 7:13-15). The secret of victory lies in knowing 'It is God working in me' (Philippians 2:13).