January is the month when our nation's pavements suddenly become crowded with an army of track-suited individuals huffing and puffing in a usually short-lived attempt to fulfil their New Year Resolution to engage in a body-shaping programme (I will avoid using the unmentionable D-word).

Superman may be vulnerable to kryptonite, but for us lesser mortals, Christmas usually exposes our weakness to chocolate – certainly in my case. And when the New Year begins, we loosen the buckles of our belts as our waistlines have become increasingly "spatially challenged" and resolve to lose a few pounds. The vast sums spent by Weight Watchers, Zumba fitness centres and the like on TV adverts at this time of year testify to how widespread the problem is.

But wouldn't it be nice if dealing with our excess physical baggage was the only kind of personal challenge we faced? But for many of us, there are also spiritual, mental and emotional forms of baggage that we carry around, and we need, just as importantly, a kind of 'Detox of the Soul' or 'Spiritual Makeover' from those debilitating aspects of our lives. Unresolved issues in our past can poison the present and rob us of our future. In Ephesians 4, the Apostle Paul speaks about the need for us to be built up, so that we will no longer be spiritual or emotional infants, but that we "become mature, attaining to the whole measure of the fullness of Christ" (Ephesians 4:13).

In another well-known passage, that great chapter on love in 1 Corinthians 13, Paul again speaks about growing up, about leaving childhood and reaching adulthood or maturity. He says in verse 11, "When I became a man, I put childish ways behind me." The verb which he uses literally means to "destroy, annihilate, put to death". He uses the same word in Romans 6 when speaking about crucifixion, the putting to death of the old self. The implication is that we have to be proactive – the habits and attitudes from which we need to be released don't just fall away by themselves. The onus is on us, with the help of God's Holy Spirit, to render them inoperative and ineffective in our lives.

The only drawback is that, like jogging or having workouts at the gym, it's hard work. Exercise is painful. Our muscles only benefit, we are commonly told, when it begins to hurt. The process of dying to self and living for Christ is similarly painful and therefore, not surprisingly, one that we try and avoid. The Christianity that is comfortable is the type that simply wants to add Jesus to our pre-existing lifestyle as a kind of supplementary fashion accessory. We continue living as we have always lived, but simply invite Jesus to accompany us, so that He's on hand to bail us out of any tough situations that may come along.

Whilst many of us give mental assent to some of the highest possible Christian doctrines and spiritual truths, in reality we are regularly defeated when it comes down to common, everyday areas of life. Determination, dedication and discipline are not always the most popular qualities amongst Christians, because we prefer convenience to obedience.

At this time of year when we make lists of the various things we aim to achieve, or change about ourselves, we would do well to plan a spiritual makeover at the same time. God's desire is for us to draw on his redeeming grace to break the chains of the past, and to take responsibility where we need to spiritually change the behaviour patterns of the present. Who said it would be easy? Certainly not Jesus, who denied himself and took up his cross, and who calls us to do likewise in following Him.

Tony Ward is a Bible teacher and evangelist who was ordained in Zimbabwe. He ministers mainly in Cardiff and Bristol.