Paul found it necessary to justify his actions because of his love for the Corinthian church and because false teachers were enticing the Corinthian believers away from Christ.
In chapters 10-12 of 2 Corinthians Paul may be responding to charges from people claiming to be apostles who arrived in Corinth and launched a vicious attack against him and his apostleship. These false teachers accused Paul of not being a real apostle or even a true Christian!
And they seemed to think he had no right to bring the gospel to Corinth because it was in their missionary territory.
These false teachers taught a different or false gospel and the Corinthians seemed willing to believe anything they told them.
Hearing of this situation, Paul asserts his apostolic authority by engaging in a discussion that is distasteful to him by boasting of his weaknesses and trials for the sake of the gospel.
While Paul’s apostolic authority is real and powerful, he says it is tempered by love for the Corinthians.
So, his boasting is not about what he has accomplished by his own abilities, but how the power of Christ has worked through him, especially through his weaknesses.
In marked contrast to the view of this world, human weakness can demonstrate God’s strength; human suffering can be a means to proclaim God’s grace.
For it is in human weakness and frailty that the power and grace of God is distinctly enabled.
- Fragile Faith – 2 Corinthians 4:7 (stevesbiblemeditations.com)