First, I don't know Joel Osteen, what he does, who he is or what he truly believes. I know that as a Christian, we are charged, each of us, to preach the Gospel of Jesus Christ. That doesn't mean necessarily from the pulpit, but if one is going to take the pulpit, this is where it starts:
And he said unto them, Go ye into all the world, and preach the gospel to every creature. He that believeth and is baptized shall be saved; but he that believeth not shall be damned. - Mark 16:15-16
The following verses make up the core tenets of The Gospel. There are many more, but each to the same effect. If Joel Osteen isn't preaching this, then I have no time for anything he might be doing in the name of Christ:
For all have sinned, and come short of the glory of God; - Romans 3:23
For by grace are ye saved through faith; and that not of yourselves: it is the gift of God: Not of works, lest any man should boast. - Ephesians 2:8-9
For the wages of sin is death; but the gift of God is eternal life through Jesus Christ our Lord. - Romans 6:23
And as it is appointed unto men once to die, but after this the judgment: - Hebrews 9:27
But the fearful, and unbelieving, and the abominable, and murderers, and whoremongers, and sorcerers, and idolaters, and all liars, shall have their part in the lake which burneth with fire and brimstone: which is the second death. - Revelation 21:8
For when we were yet without strength, in due time Christ died for the ungodly. For scarcely for a righteous man will one die: yet peradventure for a good man some would even dare to die. But God commendeth his love toward us, in that, while we were yet sinners, Christ died for us. - Romans 5:6-8
Jesus saith unto him, I am the way, the truth, and the life: no man cometh unto the Father, but by me. - John 14:6
For I delivered unto you first of all that which I also received, how that Christ died for our sins according to the scriptures; And that he was buried, and that he rose again the third day according to the scriptures. - 1 Corinthians 15:3-4
Who his own self bare our sins in his own body on the tree, that we, being dead to sins, should live unto righteousness: by whose stripes ye were healed. - 1 Peter 2:24
For Christ also hath once suffered for sins, the just for the unjust, that he might bring us to God, being put to death in the flesh, but quickened by the Spirit: - 1 Peter 3:18
Verily, verily, I say unto you, He that heareth my word, and believeth on him that sent me, hath everlasting life, and shall not come into condemnation; but is passed from death unto life. - John 5:24
For whosoever shall call upon the name of the Lord shall be saved. - Romans 10:13