“Remember.” The Greek word is idou (#2400 ἰδού), and it is used to get our attention. See commentary on Matthew 1:20 (“Look!). This could have been translated “Pay attention,” because Jesus was trying to make sure he had the attention of those he was speaking to, but given the circumstances, “remember,” is a good way to translate the word idou here (cp. HCSB).
“I am with you always.” This is a wonderful promise to believers, especially when we feel that Jesus is not with us. Life is difficult, and there is a universal spiritual war going on between the forces of light and the forces of darkness. God cannot “just make things better.” He will one day, but not right now. Furthermore, we must remember that God has to be righteous and also follow His own promises. For example, He says that as we sow we reap. So if we sow into our lives in such a way as to cause trouble for ourselves, God just cannot step in and override His own law so things will be better for us here on earth. That does not mean that Jesus is not with us, watching us and helping as best he can: he always does that, and we need to trust that he is [For more on God’s help in troubled times, see commentary on Romans 8:28].
Occasionally this verse is used to prove the Trinity because it is said that the only way that Jesus could always be with his Church is if he were God. However, that is an unproven assumption, and is not stated in Scripture. Furthermore, there are different ways of being “with” someone. For example, Scripture shows us that there is a use of “with us” that is spiritual in nature, not physical. Also, we must be careful not to underestimate the power and authority God gave Christ when He set him at His own right hand and gave him a name that is above every name. Just two verses before this one, Christ said he had been given “all authority.” God gave Christ all authority, and made Christ Head of the Church, so it is only logical to conclude that God also gave Christ the power to stay in communion with his Church.