Timothy (his name meaning ‘honouring God’) was yet a young man (1 Timothy 4:12) but one of the most faithful co-labourers of the apostle Paul. He was the son of a Greek father but had a Jewish mother named Eunice. His mother and grandmother Lois had taught Timothy the Holy Scriptures of the Old Testament from a child (Acts 16:1; 2 Timothy 1:5; 2 Timothy 3:15).
On Paul’s second missionary journey in the area of Derbe and Lystra this young believer came to the apostle’s attention (around 51 to 54 AC). This young man was well reported of by the brethren at Lystra and Iconium (Acts 16:2). During his first journey Paul had already evangelized this area and visited both these places twice (Acts 14:1; Acts 14:8; Acts 14:21). Probably this is when Timothy had heard the gospel and believed it.
Exactly in Ephesus Paul had proclaimed the whole purpose of God and in his epistle described the great privileges and blessings of the members of the body of Christ. Now he is instructing Timothy (who actually stays in Ephesus) in his first epistle in relation to the outward order of the church (whereas the first epistle to the Corinthians dealt with the inward order of the church).
The truths written in the Epistle to Ephesus not more than three years ago had no need of being repeated (1 Timothy 1:3). The apostle pre-supposed these truths as known.
This is also why the First Epistle to Timothy bears a totally different character from the Epistle to the Ephesians. First Timothy is neither directed to the believers nor to the whole church there but to a servant who had been charged and authorized by the apostle himself.