Why is this repetition"safe" for the Phillipians? Paul knows that the Gospel is a frail feather. It is easily trampelled and lost. All the lusts of our flesh war against it. So, to be "safe" he repeats the ABCs of the gospel. He assumes that we can never hear it enough.
Do you assume the same? We are no different today. In his new biography of Dietrich Bonhoeffer, Eric Metaxas, quoting a letter from Dietrich in New York to a friend in Germany (mid 1920s), writes... “In New York they preach about virtually everything; only one thing is not addressed, or is addressed so rarely that I have as yet been unable to hear it, namely, the gospel of Jesus Christ, the cross, sin and forgiveness, death and life.”
Captitulation to these distractions is possible for everyone reading this sentence. Therefore, like Paul, we should say "To write/preach/discuss the [gospel] is no trouble to me and safe for you."
 Metaxas, Eric (2010-04-20). Bonhoeffer: Pastor, Martyr, Prophet, Spy (p. 99). Thomas Nelson. Kindle Edition. A quote by Bonhoeffer describing his stay in American in 1930