Beat your plowshares into swords And your pruning hooks into spears; Let the weak say, ‘I am strong.'” Joel 3:10 (NKJV)
God calls those things which be not as though they were. Romans 4:17b.
This means God knows and says that something already is even if it is not yet seen or visible or tangible. This is faith.
In the creation of the world in the beginning, there was darkness but God did not focus on it, He did not talk about the darkness but rather said “light be or let there be light” Genesis 1:3. He spoke what was not, what wasn’t visible or apparent to the senses as being. God called an old couple who were long past child bearing, more over the woman barren, parents of multitudes of people. This was Abraham and Sarah. As far as bringing forth children they were weak or unable. But God said they were able to give birth. He even changed their names to align with what he had spoken to them. Abram became Abraham which means Father of multitudes.
It is because the Lord is the strength of the weak so they can say they are strong. The apostle Paul talks about a troublesome trial he went through which he called ” a thorn in the flesh” He pleaded with the Lord three times that it depart from him and the Lord told him “My grace is sufficient for you, for My strength is made perfect in weakness.” 2 Corinthians 12:9. This means where we are weak in our own natural human means and resources that gives opportunity and room for the Lord’s strength to be of use and take over. Paul says when he is weak then he is strong. 2Corinthians 12:10.
This means where he’s not able humanly, naturally he takes advantage of divine strength.
This is what Zechariah 4:6 implies when he says it’s not by might nor power but by my Spirit says the Lord. We do not depend on human might or power but rather rely on the strength of the Spirit of God. When we don’t know what to do then it’s an opportunity to rely on the all-knowing, all-powerful God who is able to do exceedingly abundantly above all we can ever ask or think.