May he strengthen your hearts so that you will be blameless and holy in the presence of our God and Father when our Lord Jesus comes with all his holy ones.
The word “strengthen” here means to fix, to make fast, to establish. The same word is used in vs. 2. Timothy was sent to strengthen and encourage their faith. In vs. 13, Paul pronounces a a blessing: May the Lord strengthen your hearts…. For us, the heart is the seat of salvation. God has taken away our heart of stone and given us a heart of flesh (Ezekial 36:26) It is the Lord Who fixes, makes fast, and establishes, (strengthens) the heart to walk in His ways and to do His will. I am pretty sure this means we can’t pull ourselves up by our bootstraps. Rest in Him. Trust Him to keep you steadfast.