The saying, “you can’t give what you don’t have” is from the Latin phrase ‘Nemo dat quod non habet.’ The “Nemo Dat” rule is a legal principle that a person must have ownership of property or goods before they can legally sell them.  This principal is true in the legal world, but it also holds true in the spiritual realm.
You Must Have Something Before You Can Give It Away
I have a friend who told his pastor that he wanted him to be his spiritual leader. This pastor was shocked because he had never considered this. Even though this pastor had been trained at a leading seminary, he thought he was just to manage the organization of the church. He considered himself a CEO of an organization that addressed social issues. He was not able to lead his people into the truth of the Bible because he did not know it himself. Thankfully this pastor is no longer leading a church.
The Priests Dedicated Themselves First
In the Dedication of the Wall in Jerusalem, the Priests and Levities first set themselves apart for God before doing this for the people. Nehemiah 12: 30 The priests and Levites first purified themselves; then they purified the people, the gates, and the wall. 
We Can Have the Holy Spirit Because God Gives
Just as we are told by a stewardess on an airplane trip to put the oxygen on ourselves first, we must be filled with the Holy Spirit before we can help others spiritually. Paul gives us insight into how this happens.
Ephesians 5: 15 So be careful how you live. Don’t live like fools, but like those who are wise. 16 Make the most of every opportunity in these evil days. 17 Don’t act thoughtlessly, but understand what the Lord wants you to do. 18 Don’t be drunk with wine, because that will ruin your life. Instead, be filled with the Holy Spirit, 19 singing psalms and hymns and spiritual songs among yourselves, and making music to the Lord in your hearts. 20 And give thanks for everything to God the Father in the name of our Lord Jesus Christ.
To hear more on how you can’t give what you don’t have, listen here:
https://www.armstronglegal.com.au/commercial-law/the-nemo-dat-rule/, accessed 11-23, 2021.