en_tn/2ti/02/01.md

be strengthened in the grace that is in Christ Jesus

Possible meanings are 1) "let God use the grace he gave you in Christ Jesus to make you strong" (see UDB) or 2) "encourage yourself, knowing that God has given you the grace that comes only through Christ Jesus"

among many witnesses

"with many witnesses there to agree that my words were true"

faithful

"trustworthy"