Gentleness used here describes a condition of the heart or mind. You can say that it is a gentle spirit.
Jesus was gentle and meek, but He was not weak. He blessed others out of a heart of love and compassion. In fact, Jesus and Paul both emphasized that we will have a right spirit toward others only if we approach them in a gentle, considerate spirit.
1 Thessalonians 2:7-8, “But we were gentle among you, just as a nursing mother cherishes her own children. So affectionately longing for you, we were well pleased to impart to you not only the gospel of God, but also our own lives, because you had become dear to us.”
Many people associate gentleness with weakness and that is incorrect. Being wimpy or timid are NOT products of the Holy Spirit.
2 Timothy 1:7, “But God did not give us a spirit of fear, but of power and love and of a sound mind.”
Strength and gentleness are blended together. God does not want us to treat our fellow human beings harshly…HIS nature is to be merciful, kind and gentle…and full of His power.