but the former preach Christ out of rivalry, not sincerely, because they think they are adding bitterness to my bonds.

but the former preach Christ [insincerely] out of selfish ambition [just self-promotion], thinking that they are causing me distress in my imprisonment.

But whatever former things were gains to me [as I thought then], these things [once regarded as advancements in merit] I have come to consider as loss [absolutely worthless] for the sake of Christ [and the purpose which He has given my life].