The first application that came to mind is how this could apply to RCatholic doctrine. Since Jesus is God, and this verse does say we shall see Him, as He is,...this would apply to the RC beatific vision, seeing God Face to Face. (In RC doctrine this means the believer is 'in heaven', and therefore is not in purgatory, so they 'made it'.
In your question you phrase, 'shall be like Him, because of seeing Him as He is', implying that the 'being like Him' is because of 'seeing Him as He is',..however, I do not believe the verse is saying, exactly what you are implying.
I believe the verse is making a statement, recording 'how things shall be, concerning us'.*
'We shall be like him', is stated in other places in the NT, where our new bodies are written about, 'our mortality putting on immortality'. our 'corruption putting on incorruption', and all of the other places that state we will no longer cry, be in pain, have any sickness, or even die, and all sorrow will be gone.
By saying this I am meaning that the 'shall be like Him' may refer to our new body being exactly like His resurrected and then glorified body, BECAUSE Jesus, although God, is still a human man INSIDE the Godhead. (think, ponder this, you will get my meaning)
Some bible references for this are as follows,..
Following along the RC doctrine line of thinking about this question,
an RC scholar might say that this verse supports RC doctrine, the beatific vision, including purgatorial cleansing being alluded to by the 'seeing Him as He is', it is the seeing Him as He is that may cause the purgatorial cleansing,..ie some RC's believe Purgatory could be short, 'in the twinkling of an eye', the 'seeing God' cleanses the last vestiges of 'the fall' right out of us,...making us ready for Heaven.
Protestants would not generally interpret this like I have written above, because they generally do not agree that there is a Purgatory, although Luther himself still believed in it, post RC church, although Protestant scripture says nothing about it, according to Protestants.
KJV is a translation that comes directly from the original, so I will quote it here.
1 John 3:2 King James Version (KJV)
Beloved, now are we the sons of God, and it doth not yet appear what we shall be: but we know that, when he shall appear, we shall be like him; for we shall see him as he is.
In KJV the 'because' is the word 'for', but the word is called a conjunction,... connective, and may not mean 'because', exactly, or, it may (See Strong's G3754 ὅτι).