Romans 8:15

For you have not received a spirit of slavery leading again to fear (of God’s judgment), but you have received the Spirit of adoption as sons (the Spirit producing sonship) by which we (joyfully) cry, “Abba! Father!”

Our thoughts can lead us into slavery of fear if we allow them. We can keep our minds in faith when we monitor our thoughts and think with purpose and not random. We need to build our faith in Jesus and what we have through His death on the cross and salvation, making God our Father.