Timothy was a very young pastor with a very important position, that of pastoring the vital and large church in Ephesus. He was also having a very tough time. There were various power-blocs in the church who were trying to gain control of the congregation in Paul's absence. They resented Paul's choice of Timothy as pastor and did everything they could to discredit and intimidate the young man.
Apparently they were succeeding. Timothy was so intimidated that he had actually become "ashamed" as a preacher and had even become "ashamed" of Paul (see v.8 — part of the intimidation tactic was to question Paul's integrity: some of them ridiculed his continual predisposition to being thrown in jail —see v.12, 15, 16, 2:9, 4:16). Timothy's ministry had become characterized by a spirit of "timidity". The flame of his calling had almost died — there was a mere whisper of smoke where a fire had once burned.
That's why paul reminds Timothy to "fan into flame the gift of God" which is in him (v.6 — NIV). This is to be more than mere bravado; rather it's to be done in the context of the "spirit" God has given him.
God has given him the "power" to be bold and assertive in preaching. He has given him the "love" to be effective in pastoring, and He has given him the capability to be "self-disciplined". With these "givens" comes responsibility — and Paul expects Timothy to get out of his shell and back into battle.