1 Peter 3:15
We may be called upon to answer that question when asked by an atheist or an agnostic or skeptic. My reasons are many. I could point to the Bible itself as evidence that God exists, but to the atheist or agnostic, this evidence is likely to be discounted as irrelevant. I do not believe that the Bible as evidence for the existence of God would be a good place to start.
The evidence from the Bible is great in convincing those who believe in a "cosmic creator/ designer" that Jehovah is God, but it will not convince the atheist that there is "a God."
So to begin a discussion with such an individual, one would have to look outside of the Bible and use some external evidence as a starting point. There are certain arguments that are more or less philosophical or logical in nature than they are Biblical or scientific. These arguments are backed by science and the Bible, but can also stand on their own as proof that there is "a god." These arguments have been around in one form or another for millennia: the Cosmological Argument, the Teleological Argument, the Anthropological Argument and the General Argument for the existence of God.
The Cosmological Argument for the Existence of God
Let's begin with the Cosmological Argument for the Existence of God. This term, Cosmological, stems from the Greek word, kosmos, which refers to the world or even the universe itself, which is also how the English word "cosmos" is defined. The Cosmological Argument is a logical argument from the standpoint of cause and effect –that for every effect there must be a sufficient cause. The Cosmological Argument can be stated as follows: The universe exists (the effect is observed); therefore there must be a sufficient cause (God).
Scientists have proof that the universe, as we know it, is not eternal – that it has a root cause. This is where the theory that billions of years ago a "big bang" came along and the universe as we know it came into existence. The problem with this is where did the "thing" that went "bang" come from and what caused its explosion? Something had to have existed before the "big bang," before the universe existed. The atheist can argue that there was another, similar, yet much smaller explosion that took place before the "big bang," which created that "thing" which exploded and brought our universe into being.
That still leaves the same questions, only pushed back by billions of years. Think about it this way, if you will. If the universe itself is the oldest "thing" in existence, but it is known to have had a cause, then it follows something must have existed prior to the existence of the universe. Ultimately, it must be argued that something has always existed, that its existence is not dependent upon something else and that it is sufficient in power to cause the effect that we see – the universe. Something that is eternal and powerful – God, the Uncaused, Cause of everything!
The Teological Argument for the Existence of God
Next, let's explore the Teleological Argument for the Existence of God. This argument gets its name from the Greek word, teleos, which describes something that is complete or finished. This is an argument from design. If you were to look on the inside of a mechanical clock or pocket watch you would observe a host of very small and tightly fitted pieces that each work together in a very detailed way. You could not look at that precision instrument and come away with the belief that it just came together on its own. The design of the watch necessitates a designer.
Now if we were to look on a cosmic scale and observe the universe with its unvarying laws, such as the law of gravity and the laws of thermodynamics, we would see that the various heavenly bodies interact with one another in very predictable ways. So fixed are these laws, that astronomers can chart where each heavenly body is located relative to the Earth at any given time for thousands of years into the past and into the future.
Another evidence of design is noted in a large number of variables that each had to come together in precisely the way they have in order for life to exist on the earth. For instance is the Earth was slightly further from the sun the temperatures would be entirely too cool for life to exist and if it were slightly closer it would be too hot. Other variables include the angle upon which the earth rotates on its axis, the distance of the Earth from the moon and the size of the moon, etc.
Look also at the human body on a cellular level, the body with all of its member, the eye, the muscular system, the circulatory system, etc. When all of this is taken into account, how can one deny that there is a Designer? Combine this concept with the Cosmological Argument: If the design we see in the universe is the effect, then what is the sufficient cause behind such a gargantuan mountain of teleological evidence? Again, there MUST be a God!
The Anthropological Argument for the Existence of God
Another thing to consider is what is known as the Anthropological Argument for the Existence of God. This, again, derives from a Greek word and that word is Anthropos, which means "humankind." This argument takes into consideration that there is a universal human code of morality. In all of the Earth, there has never been discovered a civilization or group of people that have not had a sense or moral "ought." No culture has ever said that man "ought" to steal from his neighbor or that a man "ought" to kill his neighbor!
In fact, in every culture, there is a distinct "ought not" with both of these actions.
There is a universal concept of justice with every people or culture, the details of which may differ slightly from one people to the next, but there will be a clear concept nevertheless. This argument is especially strong in dealing with the theory of evolution because there is no evolutionary reason why this concept should have ever been developed by man. The "law of the jungle" would prevail to this day if it were not for man's innate moral sensibility.
From where did this moral sensibility originate, if it did not come from evolution? Again, this points to a Creator of a moral nature. That Creator is God.
The General Argument for the Existence of God
Similar to the Anthropological is what has been termed as simply the General Argument for the Existence of God. This is based on the universal instinct toward worship that mankind possesses. Like with the previous argument, there has never been discovered a people or culture anywhere on the face of the earth that did not worship something.
Only in our modern world are there found those who deny that "a god" exists, but historically that was never true! Ask yourself, "Where would mankind have even developed the concept of "a god," if it were not for the God revealing Himself?
Where would the concept of "spirit" have evolved from? Or from, where would the idea of a Being possessing an "eternal" nature have derived? Combine this with what is designated as the Esthetical Argument for the Existence of God, which asks the question of from where did the existence of beauty and man's appreciation for beauty spring?
There is no solid evolutionary reason for the existence of these concepts. Why would they have evolved? The answer is that without God they would not have come into the human psyche!
Looking at just a few of these arguments and combining the concepts involved, one can come to only a single logical conclusion – there is a God! Once a person can be convinced of this in their mind, then they would be more likely to accept the Bible as a source of evidence that Jehovah is that God! Through what is known as General Revelation – that is our observation of evidences such as first cause, design, humankind's moral sensibility and the concept "god-hood" and appreciation for beauty – we can know that there is "a god, " but the only through Special Revelation (the word of God) can we know who that GOD is and what He desires of us!
There is, perhaps, one more thing to consider – Pascal's Wager. Pascal was a French theologian who quite succinctly stated the following rhetorical questions:
"If there is no God and I choose to conduct myself as if there is a God, then what would be the eternal consequences? And conversely, if there is a God and I choose to conduct myself as if there is no God, then what would be the eternal consequences?" -Pascal
Are you willing to bet your eternal soul on Pascal's Wager?