In 2 Timothy 2:1 Paul told Timothy to be strong in the grace that is in the Lord Jesus Christ.
The word for be strong is "endunamoo" in the Greek and it means to be empowered, be made strong, or enabled.
In the Greek grammar it's a Present – Passive – Imperative.
It's meaning is that it's imperative that we are to continually receive the action of being strengthened by grace. We don’t pull ourselves up by the boot straps and buckle up as a soldier to strengthen ourself but we are strengthened by grace.
Too often we try to strengthen ourselves for the "thorn in the flesh" (2 Cor 12:7) but the answer is learn that God's grace is sufficient and God's strength is made perfect in our weakness (2 Cor 12:9).