For by the grace (unmerited favour of God) given to me I warn everyone among you not to estimate and think of himself more highly than he ought [not to have an exaggerated opinion of his own importance], but to rate his ability with sober judgment. Romans 12:3 (AMPC)
When we talk about relationships, we have to distinguish between two categories: vertical and horizontal. Your vertical relationship is the one you have with God. He loves you so much that you could never begin to comprehend the extent of it. You are incredibly special to God.
Your horizontal relationships refer to your ties with other people. Romans 12:3 pertains to these horizontal relationships when it tells you not to think too highly of yourself or exaggerate your importance. It isn’t referring to your confidence in how special you are to God.
As you become more confident in God’s love and acceptance, be careful that you don’t become arrogant or brash with those who are struggling. If you have overcome a struggle in your life or have never struggled in an area, it may be easy to judge others if they are still struggling in that area. For example, if you once struggled with your weight but you did what it took to lose it, you might look down on people who are still overweight. We can’t take the attitude that others should just snap out of their problems.
As you allow God to increase your confidence, keep these two things in mind. You can think as highly of yourself as you want as long as you give God all the glory and you esteem everyone else to be greater than you.