It is true that those that have nothing of the Spirit of Christ in them are not his. That is that they do not belong to Christ, they have no part in his inheritance; and to put it bluntly they are not sons or daughters of God because they have not received Christ. John 1:12-13 says ‘But to all who did receive him, who believed in his name, he gave the right to become children of God, who were born, not of blood nor of the will of the flesh nor of the will of man, but of God.’
Those that do not have the Spirit of Christ in them are not born of God, they are still in their flesh and possess nothing of that sweet Spirit for it is written (John 3:6) ‘That which is born of the flesh is flesh, and that which is born of the Spirit is spirit.’ Man is naturally from birth born of the flesh possessing nothing, not even an ounce of the Spirit for it is yet to be born of the Spirit or of God. Those that do possess the Spirit are those that Christ claim to be his, for it is also written 1 John 3:24 ‘And by this we know that he abides in us, by the Spirit whom he has given us’ and also Rom 8:9-10 ‘You, however, are not in the flesh but in the Spirit, if in fact the Spirit of God dwells in you. Anyone who does not have the Spirit of Christ does not belong to him. But if Christ is in you, although the body is dead because of sin, the Spirit is life because of righteousness.’
Those that belong to Christ posses his Spirit in them and if it is by this that we know that we belong to Christ then surely everybody who claim they belong to Christ must have this Spirit in them. And this Spirit is Holy for it is written (Eph 1:13) ‘In him you also, when you heard the word of truth, the gospel of your salvation, and believed in him, were sealed with the promised Holy Spirit.’ This Spirit which indwells those who belong to Christ yields fruit in them as prescribed in Galatians 5:22-23 ‘But the fruit of the Spirit is love, joy, peace, patience, kindness, goodness, faithfulness, gentleness, self-control; against such things there is no law.’ And Christ himself said of the necessity of bearing fruit in his final discourse to his friends before his crucifixion (Joh 15:2) ‘Every branch in me that does not bear fruit he takes away, and every branch that does bear fruit he prunes, that it may bear more fruit.’ And also (Joh 15:16) ‘You did not choose me, but I chose you and appointed you that you should go and bear fruit and that your fruit should abide, so that whatever you ask the Father in my name, he may give it to you.’
Dear reader, sinner or saint; ask yourself the solemn question, ‘Do I have the Spirit of Christ in me? Have I produced fruit? By fruit it could be one or many for some yielded a hundredfold, some sixty and some thirty. This question should cause us to wail if we are found not to have the Spirit of Christ in us but we should be glad because it is not yet too late. We, like the tax collector should beat our breast and cry to the Almighty Loving God ‘have mercy on me a sinner, cause my heart to be born again.’ And if we are found to possess that sweet Holy Spirit which seals our belonging to Christ then let us rejoice and be glad, going from glory to glory and be of our daily task in living all for his glory and labouring in ways in which we can bring miserable sinners to Christ, so that they can join in our happy feast when this world and all of its vanities will be swallowed up in eternity.