What Does It Mean For God to be Infinite?
When a Muslim raises this question, the Christian should return it with another question: "Why can't an infinite God be united with the finite?" Think about the assumptions that are lying behind the question: The question assumes that God is infinite in terms of size, mass, etc (therefore it is impossible to take an infinite amount of something and put it in a finite object). When one says that God is infinite, one is referring to a metaphysical reality, not a physical one -- i.e. to an immaterial, incorporeal, non-spatial understanding of the infinite. In any case, the infinite does not exist in the material universe as a concrete object. God's essence may therefore be described as qualitatively infinite. Why, then, can't an incorporeal, immaterial, non-spatial Being unite to his Person a physical body? Indeed, even in the Old Testament Scriptures we find that the fullness of the divine essence was to be found in the Holy of Holies, in the Ark of the Covenant, and in the Angel of the Lord figure (which I wrote about here).
The Omnipresence of Christ
The Muslim might come back at this point and argue that God cannot be omnipresent and not omnipresent at the same time -- this would present a logical contradiction. When dealing with this objection, it is of utmost importance that we are careful to define our terminology. What does it mean to be omnipresent? Does omnipresence mean to be present everywhere in a material, substantial sense? Of course not. If God is not a material, spatial being then he cannot be materially, spatially present anywhere. What, then, does it mean to be omnipresent? Omnipresence refers to the fact that the creation is present before God since there is no part of creation that he does not oversee, sustain and superintend. All of creation is under his control and providential guidance. Therefore, why can't God unite to himself a temporal, physical body and still oversee the entire creation?
Indeed, on many occasions throughout the gospels, Jesus appears to be able to perform miracles from afar, without his body being physically present. For instance, in Mark 7:24-30, Jesus casts out the demon from a girl without being physically present. In John 1:45-49, Jesus says that he saw Nathaniel sitting under the fig tree even though He was not Himself present physically. In John 4:43-54, a man's son was healed by Jesus without Jesus being physically present. In Matthew 8:5-13, a centurion's son is healed -- again, without Jesus being physically present. In all of those examples, it is Jesus who is healing and seeing people from great distances. That being the case, what is the problem with Christ taking on a spatial, physical body and still overseeing the entire creation? It thus presents no contradiction to posit that Christ be "omnipresent" while still being spatially located at the same time.
The Omniscience of Christ
But surely, the Muslim might respond, Jesus was ignorant of certain things such as the date of His return (Matthew 24:36; Mark 13:32). How, then, can Jesus have been omniscient and non-omniscient at the same time? I actually do not think that this is quite as paradoxical as it might at first appear, since it is possible that Christ may have known certain things in his waking, conscious knowledge while possessing exhaustive knowledge in his subconscious knowledge. At the point of the incarnation, Jesus submitted Himself to the Father as a servant (see my previous article here for more on this). Jesus self-identifies as God's servant, for instance, in Matthew 12:18. In John 15:15, Jesus says, "the servant does not know what his master is doing." If Jesus was the servant of the Father, then it stands to reason that the Father may well have veiled from the Son certain truths during His earthly ministry. In John 21:17, Peter says to Jesus, “Lord, you know everything; you know that I love you.” Jesus does not correct Peter on this point. This suggests that Jesus, in His glorified state, post-resurrection, does once again know all things.
My argument draws further support from John 16:25-31, in which we read,
"“I have said these things to you in figures of speech. The hour is coming when I will no longer speak to you in figures of speech but will tell you plainly about the Father. In that day you will ask in my name, and I do not say to you that I will ask the Father on your behalf; for the Father himself loves you, because you have loved me and have believed that I came from God. I came from the Father and have come into the world, and now I am leaving the world and going to the Father.” His disciples said, “Ah, now you are speaking plainly and not using figurative speech! Now we know that you know all things and do not need anyone to question you; this is why we believe that you came from God.” Jesus answered them, “Do you now believe?”"It is the same Greek used in 16:30 that is used in 21:17. So, this means that Jesus' omniscience was still in his possession, even though it was veiled from him having full access to it.
In conclusion, when dealing with the question of whether the infinite God could become joined to a physical body in the man Christ Jesus, one has to be careful as to one's use of terminology. We do not believe that God is infinite in the sense of possessing infinite mass or that God is infinite in a spatial, material sense. Rather, God is qualitatively infinite, and there is no logical reason why the infinite God cannot join Himself to a physical body.