That one God might have three aspects is no stranger than a single man haveing two hands, so the Trinity makes sense to me.
However that may be right or wrong, it is definately not one of the things one must beleive to be saved or to be considered a Christian.
Its importance is as an attempt to be logical , which I think Jesus specificly stated is not a requirement.
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The Trinity does not say "God in three aspects": it says "God in three PERSONS".
Any fool can see that a man has two hands. Seeing that the same being is really three different entities: two of them totally invisible, one that only pops in once in 2000 years, promises to return and then doesn't, well that takes major amounts of faith, or self-delusion, depending on your point of view.
If you don't believe in the Holy Spirit, which is the least mentioned and vaguest of the three parts of the Trinity, you are in a world of hurt, says the Bible:
Truly I say unto you, All their sins shall be forgiven unto the sons of men, and whatever blasphemies they utter: but whoever blasphemes against the Holy Spirit never has forgiveness, but is guilty of an eternal sin: because they say, ‘He has an unclean spirit’. Mark 3:28-29
Therefore I tell you, every sin and blasphemy will be forgiven men, but the blasphemy against the Spirit will not be forgiven. And whoever says a word against the Son of man will be forgiven; but whoever speaks against the Holy Spirit will not be forgiven, either in this age or in the age to come. Matthew 12:30-32
For it is impossible for those who were once enlightened, and have tasted of the heavenly gift, and were made partakers of the Holy Ghost, And have tasted the good word of God, and the powers of the world to come, If they shall fall away, to renew them again unto repentance; seeing they crucify to themselves the Son of God afresh, and put him to an open shame. For the earth which drinketh in the rain that cometh oft upon it, and bringeth forth herbs meet for them by whom it is dressed, receiveth blessing from God: But that which beareth thorns and briars is rejected, and is nigh unto cursing; whose end is to be burned. Hebrews 6:4-9
If we deliberately keep on sinning after we have received the knowledge of the truth, no sacrifice for sins is left, but only a fearful expectation of judgment and of raging fire that will consume the enemies of God. Hebrews 10:26-27