I don't think Pascal intended the Wager to be pulled from Pensées and used as an independent, discrete argument for God. But don't take my word for it, here's what the man says himself:
Let us now speak according to natural lights.
If there is a God, He is infinitely incomprehensible, since, having neither parts nor limits, He has no affinity to us. We are then incapable of knowing either what He is or if He is. This being so, who will dare to undertake the decision of the question? Not we, who have no affinity to Him.
Who then will blame Christians for not being able to give a reason for their belief, since they profess a religion for which they cannot give a reason? They declare, in expounding it to the world, that it is a foolishness, stultitiam; and then you complain that they do not prove it! If they proved it, they would not keep their word; it is in lacking proofs, that they are not lacking in sense. "Yes, but although this excuses those who offer it as such, and takes away from them the blame of putting it forward without reason, it does not excuse those who receive it." Let us then examine this point, and say, "God is, or He is not." But to which side shall we incline? Reason can decide nothing here. There is an infinite chaos which separated us. A game is being played at the extremity of this infinite distance where heads or tails will turn up. What will you wager? According to reason, you can do neither the one thing nor the other; according to reason, you can defend neither of the propositions.—Pensée 233
Stultitiam is Latin meaning folly and is a direct reference to:
For since, in the wisdom of God, the world did not know God through wisdom, it pleased God through the folly of what we preach to save those who believe.—1st Corinthians 1:21 (ESV)
In other words, Pascal rejects the Aquinian project to prove God and proceeds to defend the Christian's warrant1 to nevertheless believe that "God is". It is a practical demonstration of the flaws of René Descartes' skepticism. Life is more complicated than merely acting on true beliefs and not acting on false ones. In fact we generally don't know the outcome of our decisions until long after they are made.2 But that doesn't prevent us from making those decisions—Pascal asserts that by merely existing, we must make the Wager; we must decide what our purpose in life is to be.
Pascal's further point is that even when we don't know the probabilities, the payoff of one of the choices may be so large as to make the decision of which horse to bet on easy. Again, let's let him speak:
The end of this discourse.—Now, what harm will befall you in taking [the Christian] side? You will be faithful, honest, humble, grateful, generous, a sincere friend, truthful. Certainly you will not have those poisonous pleasures, glory and luxury; but will you not have others? I will tell you that you will thereby gain in this life, and that, at each step you take on this road, you will see so great certainty of gain, so much nothingness in what you risk, that you will at last recognise that you have wagered for something certain and infinite, for which you have given nothing.
Pascal argues that even if God is not, giving up "poisonous pleasures" will cost nothing since they will be replaced by other pleasures in this life. So the Wager isn't so much believing in order to avoid the loss of heaven, but substituting one type of pleasure for another in the expectant hope of an infinite reward. In fact, he seems to be giving the same advice that David gave:
Oh, taste and see that the LORD is good!
Blessed is the man who takes refuge in him!
Oh, fear the LORD, you his saints,
for those who fear him have no lack!
The young lions suffer want and hunger;
but those who seek the LORD lack no good thing.
—Psalm 34:8-10 (ESV)
Pascal isn't arguing that the Christian life is something to be entered into on the off chance that we will win the cosmic lottery. Rather, he is proposing that Christians are not wrong to believe what they cannot prove. Or as Jim Elliot wrote:
He is no fool who gives what he cannot keep to gain that which he cannot lose.
For a more comprehensive defence, see Alvin Plantinga's Warranted Christian Belief.
One of the most monumental decisions in my life was to attend UCLA to study Atmospheric Sciences. But the ripple effects of that decision are still not settled. I've already won the bet in the most unexpected ways, including finding my wife.