The Bible is filled with people God used despite their weaknesses, failures, and sometimes very serious mistakes.
Why do you think God chooses to accomplish His purposes through imperfect human beings rather than only through people who seem especially righteous or capable?
What does that tell us about God and about the kind of people He can use?
It is very simple and Paul says it. ’ I am the chief of sinners.-
or Chesterton replying to a Times article about what is wrong with the world wrote. " Dear Editor, In answer to what is wrong with the world , ’ I Am’."
or as the bible says ’ ALL have sinned and fallen short of the glory of God.’
God uses fallen men and women because that is all there is, there are no sinless people, and those who claim they do not sin are as 1John1:10 says If we claim we have not sinned, we make him out to be a liar and his word is not in us..
So be encouraged that you are no different from any of yhe great saints of old or recent times, you like them are a sinner who can be used by God, it just takes faith to act or speak and keep acting or speaking.
I have read where God answers this question at many times, to more than a few people, at various places in our Bible, but none answer this question any better than the Apostle Paul in his letter to the Corinthians.
For you see your calling, brethren, that not many wise according to the flesh, not many mighty, not many noble, are called. But God has chosen the foolish things of the world to put to shame the wise, and God has chosen the weak things of the world to put to shame the things which are mighty; and the base things of the world and the things which are despised God has chosen, and the things which are not, to bring to nothing the things that are, that no flesh should glory in His presence. But of Him you are in Christ Jesus, who became for us wisdom from God–and righteousness and sanctification and redemption-- that, as it is written, “He who glories, let him glory in the LORD.” (1 Corinthians 1:26-31)
If I may add one feeble editorial to your question, you said:
Some of the answer to this question surely lies in our mistakenly-worldly idea of what perfection looks like. It is made quite obvious in our scriptures that God has a very different idea of what a perfectly suitable servant looks like. One of the places where this concept is poignantly illustrated is in the very familiar story of the anointing of David.
So it was, when they came, that he looked at Eliab and said, “Surely the LORD’S anointed is before Him.” But the LORD said to Samuel, “Do not look at his appearance or at the height of his stature, because I have refused him. For the Lord does not see as man sees; for man looks at the outward appearance, but the LORD looks at the heart.” So Jesse called Abinadab, and made him pass before Samuel. And he said, “Neither has the LORD chosen this one.” Then Jesse made Shammah pass by. And he said, “Neither has the LORD chosen this one.” Thus Jesse made seven of his sons pass before Samuel. And Samuel said to Jesse, “The LORD has not chosen these.” And Samuel said to Jesse, “Are all the young men here?” Then he said, “There remains yet the youngest, and there he is, keeping the sheep.” And Samuel said to Jesse, “Send and bring him. For we will not sit down till he comes here.” So he sent and brought him in. Now he was ruddy, with bright eyes, and good-looking. And the LORD said, “Arise, anoint him; for this is the one!” Then Samuel took the horn of oil and anointed him in the midst of his brothers; and the Spirit of the LORD came upon David from that day forward. So Samuel arose and went to Ramah. (1 Samuel 16:6-13)
It may seem like God does not choose his servants wisely at times, but The LORD reminds Samuel (v7) that His divine ability to see deep into the heart of his chosen makes his choosing perfect. The second aspect that assures the perfection of God’s choosing comes in V13 of the same passage. God takes what looks like an insufficient vessel and pours His enabling Spirit onto it. God’s enabling could make even rocks cry out (Luke 19:40) in praise of His perfection. These two familiar stories are just examples of our Savior’s preemptive response to your query.
Humbly
KP