Because two different “wills” are involved – the will of God and the will of US. These two wills are completely different. God’s will is to look after the interests of ALL, while OUR will is to look after the interests of OURSELVES. Everything on the natural scale tells us to look out for “number one”, because we know no better. But if we have any moral appreciation at all, with maturity we may recognise that it is better if the interests of just more than ourselves is applied in situations where the common good is the more realistic option.
On this question appears to hinge the difference between eternal death or eternal life. If we consider the two aspects of “The works of the flesh” and the “Fruit of the Spirit” we get to see some difference between the two states. Then there is also the “in-between” state, the one where ‘normal decent good people live?’
Jesus seemed to say there were no in-betweens, that if people were “lukewarm” they would be ‘spewed out of His mouth.’
It appears that there are two states of being, and we better be in the right one, and FULLY so, not just “halfway”. But how can one be “halfway” anyway, when the two choices are either righteousness, or NOT righteousness?
So God is a force always working for the good of all, but we in out natural state are far more likely to be working for our own good in every possible way. Only because it is convenient to include others at times, do we do so, usually because of some kind of “you scratch my back and I’ll scratch yours”. And even when it appears we may be acting out of some form of kindness to others, this is usually limited to the particular situation at the time. There is often vested interest somehow involved.
But God calls for us to give up our own lives, to give up our independence and autonomy of living, in order to serve His interests rather than our own. He expresses the seriousness of this matter by the demonstration of His own Son dying willingly to serve the love of His Father. Because love is the highest calling, is the highest form of existence, and only as we act in Love are we acting in the interest of all, because this is the will of God, that He being love should be given this expression by His creation in all circumstances.
Our own self interest will never act in accordance with God’s design creation, will never produce those elements of self sacrificing love which is the basis of all of God’s creative purpose.
Self interest has the effect of destroying God’s interest, self interest produces thoughts and actions which drag other people down instead of building them up. The expressions of self interest work directly to destroy the nature of God as revealed in the creation itself. We are either servants of self, in which case we are opposing God, or we are servants of God in opposition to any self interest no matter where it springs up from.
Self interest works against the building up of the nature of God inside ourselves, it works against the activity of Christ outworking from us which otherwise would have resulted from Him being allowed to rule in our hearts. People ask what God’s will is, but it is very simple, it is to LOVE.